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Digitized  by  tine  Internet  Arciiive 

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http://www.ar.chive.org/details/descriptiveanatoOOblac 


X 


Descriptive  Anatomy 


OF  THE 


Human  Teeth. 


^^,     \ 


BY 

G.  V.  BLACK,  M.D.,  D.D.S. 


PUBI^ISHED   BY 

The  Wilmington  Dbntai,  Manufacturing  Co.  , 
14 1 3  Fii^BKRT  Street, 

PHILADEIvPHIA,    PA. 
Copyrighted,  1890,  by  The  Wilmington  Dental  M'fg  Co.,  Phila. 


PREFACE. 

BY  my  experience  as  a  practitioner,  as  a  teacher,  and  in 
my  intercourse  with  fellow  practitioners,  I  have  be- 
come convinced  of  a  serious  defect  in  the  teaching 
of  the  details  of  the  anatomy  of  the  teeth,  and  in 
the  systemization  of  the  terms  used  in  their  description. 
This  defect  has  been  a  constant  drawback  at  the  chair,  in  the 
laboratory,  and,  most  of  all,  in  the  college.  The  object  of 
the  present  volume  is  to  remedy,  in  a  measure,  this  defect. 
To  this  end  I  have  had  constantly  in  view  the  needs  of  the 
dental  student  and  practitioner. 

We  have  heretofore  had  excellent  general  descriptions  in 
human  and  comparative  dental  anatomy  ;  but  these  have 
dealt  principally  with  the  general  forms  of  the  dentitions  of 
the  mammalia  and  other  orders  of  animate  beings,  rather 
than  with  specific  descriptions  of  the  forms  of  the  various 
surfaces,  and  surface  markings,  making  up  the  sum  of  the 
forms  of  the  individual  teeth  of  man.  Valuable  as  these 
works  have  been,  they  have  left  the  acquirement  of  a  knowl- 
edge of  the  details  of  the  specific  forms  of  the  human  teeth 
mostly  to  individual  observation.  By  this  means,  many  have 
attained  to  an  excellent  perception  of  the  various  forms  of 
the  human  teeth ;  but  it  is  not  reasonable  to  suppose  the 
profession  generally  will  do  this  without  some  fixed  guide. 
"What  the  dental  student  wants  most  in  the  college,  and  in 
the  office,  is  a  systematized  nomenclature  of  the  several  parts 


PREFACE. 


of  the  teeth  in  detail ;  and  such  a  description  as  will  call  his 
attention  successively  to  every  part  of  each  tooth,  as  Gray,  in 
his  Anatomy,  has  called  attention  to  every  part  of  each 
bone,  however  apparently  unimportant.  It  should  be  re- 
membered that  anatomy  is  not  to  be  learned  from  books 
alone,  but  also  by  bringing  the  parts  to  be  studied  into  view, 
and  closely  examining  them  in  connection  with  the  descrip- 
tions given.  Any  one  who  may  read  the  present  volume 
without  a  reasonable  number  of  human  teeth  of  each  denomi- 
nation before  him  for  examination  and  comparison,  will  be 
but  partially  benefited. 

It  has  been  my  object  to  systematize  the  nomenclature 
most  in  vogue  with  the  profession,  whenever  practical,  rather 
than  to  introduce  new  terms.  However,  the  reader  will  find 
a  few  new  terms,  and  possibly  a  few  old  ones  that  are  used 
differently  from  the  former  custom.  The  terms  up  and 
down,  to  indicate  direction  or  parts  of  teeth,  are  abandoned, 
because  of  their  ambiguity.  In  a  few  instances,  new  forms 
of  old  words  have  been  used,  especially  to  avoid  the  terms 
inner,  outer,  backward,  forward,  etc.,  which  are  so  often  mis- 
leading. The  words  mesial,  distal,  labial,  buccal,  lingual, 
etc.,  are  used  as  ad  Verbs  of  direction  by  adding  /y,  or  the 
same  thing  is  accomplished  by  the  use  of  the  preposition  to. 
It  is  as  easy  to  say  of  a  cavity  that  it  extends  far  beyond, 
beyond,  to,  or  nearly  to,  the  gingival  line,  as  to  say  it  ex- 
tends up  or  down,  etc.,  and  the  meaning  will  not  be  mistaken ; 
or  to  say  that  a  cavity  extends  distally,  or  to  the  distal,  or 
lingually,  or  to  the  lingual,  instead  of  backward,  or  inward, 
either  of  which  have  different  meanings  in  different  situa- 
tions.    The  best  rule  is  to  use  no  extraneous  object  in  the 


PREFACE. 


designation  of  the  parts  of,  or  direction  on,  the  surface  of  a 
tooth ;  but  to  confine  the  phraseology  to  the  specific  and 
well  defined  terms  applied  to  its  several  parts.  The  back 
part  of  a  molar  would  not  mean  the  same  relative  part  as  the 
back  part  of  an  incisor.  In  many  such  ways  the  author  has 
endeavored  to  systematize,  and  make  more  definite,  the 
phraseology  applied  to  the  teeth  without  going  to  extremes, 
knowing  well  that  forms  of  language  once  in  use  can  be  im- 
proved more  easily  than  they  can  be  displaced  by  new  terms, 
though  more  exact. 

The  absence  of  a  Bibliography  may  be  noted.  The  plan 
and  object  of  this  work  has  not  seemed  to  call  for  many 
references  to  authorities.  This  does  not  imply,  however, 
that  authors  who  have  preceded  me,  as  Fox,  Carabelli, 
Tomes,  Wedl,  Judd,  Wortman,  and  many  others,  to  whom 
we  are  greatly  indebted,  have  been  either  overlooked  or 
ignored. 

The  illustrations  have  all  been  made  by  the  author  for 
the  23u.rpose  of  illustration,  rather  than  as  works  of  art. 
After  experimenting  with  the  various  plans  of  the  manage- 
ment of  light  and  shade,  diffuse  light  has  been  used  because 
more  detail  could  be  shown,  esjDCcially  in  the  difficult  task 
of  illustrating  the  occluding  surfaces  of  the  teeth.  Each 
picture  of  the  teeth,  in  all  its  details,  is  drawn  from  accurate 
measurements  of  the  particular  tooth  in  hand. 

Much  of  dental  histology  might  properly  find  place  in 
this  book ;  but  that  subject  is  well  rejjresented  by  others. 
Malforms  of  the  teeth,  supernumerary  teeth,  and  variations 
of  arrangement,  belong  to  the  subject  of  irregularities,  which 
is  amply  treated  by  several  authors.     Our  aim  has  been  to 


6  PREFACE. 


confine  the  book  strictly  to  normal  macroscopic  anatomy. 
However,  a  very  serious  difficulty,  which  has  always  met  the 
dental  anatomist,  has  been  the  variations  of  form  met  in 
teeth  of  the  same  denomination.  The  endeavor  has  been  to 
systematize  these  under  one,  two,  or  more  typical  forms  of 
each  tooth,  or  its  lobes,  and  point  to  the  character  of  the 
changes  which  occur.  This  has  occasionally  led  to  the  men- 
tion of  abnormal  forms. 

The  reader  will  find  scattered  through  the  work  some 
hints  with  regard  to  the  practical  bearing  of  anatomical 
points  on  operative  procedures,  which  it  is  hoped  will  be  of 
value. 


DENTAL  ANATOMY. 

1.  Man's  food  is  both  animal  and  vegetable,  and  his 
teeth  are  so  formed  as  to  enable  him  to  readily  masticate 
either  kind ;  therefore,  his  teeth  differ  from  those  of  both  the 
carnivorous  and  herbivorous  animals,  and  form  the  type  of 
the  omnivora.  They  are  formed  for  catting,  tearing,  and 
comminuting  many  kinds  of  food.  The  incisiors,  situated 
anteriorly,  have  edges  for  cutting ;  the  cuspids  and  bicus- 
pids, at  the  angles  of  the  mouth,  have  fairly  sharp,  though 
not  very  long,  points  or  cusps,  well  calculated  for  tearing ; 
while  the  molars,  situated  in  the  posterior  part  of  the  mouth, 
have  broad,  tuberculated  grinding  surfaces,  which  serve  well 
to  grind  or  comminute  the  more  solid  masses.  The  forms 
of  the  teeth  of  man  indicate  a  design  that  his  food  should 
be  taken  in  rather  small  masses,  considered  from  the  stand- 
point of  the  habits  of  animals  in  general,  and  that  it  should 
be  very  thoroughly  commingled  with  saliva  before  being" 
passed  to  the  stomach. 

2.  The  adult  has  thirty-two  teeth,  as  follows :  In- 
cisors, f;  cuspids,  \;  bicuspids,  |;  molars,  §  =  32.  The 
teeth  are  composed  of  four  tissues:  enamel,  which  covers 
the  crown ;  dentine,  which  forms  the  body  of  both  crown 
and  root;  cementum,  which  covers  the  roots  and  joins 
with  the  enamel  at  the  gingival  line,  or  neck,  of  the 
tooth ;  and  pulp  tissue,  which  fills  the  central  cavity  of  the 
dentine. 

3.  Each  tooth  presents  for  description  certain  charac- 
ters common  to  all,  such  as  crown,  neck  or  gingival  line^ 
root,  pulp-chamber,  canal,  and  surfaces  of  crown  and  root. 
The  crown  of  a  tooth  is  that  part  which  projects  beyond 

7 


8  NOMENCLATURE. 


the  gum  tissue,  and  is  covered  with  enamel ;  while  the  root, 
covered  with  cementum,  is  that  portion  fixed  in  the  bony 
process  of  the  jaw,  by  which  the  whole  tooth  is  held  securely 
in  position.  The  root  of  a  tooth  may  be  single,  as  in  the 
incisors  and  cuspids  ;  divided  into  two  prongs  or  roots,  as  in 
the  lower  molars ;  or  into  three  roots,  as  in  the  upper  molars; 
'Or  into  a  greater  number,  as  in  exceptional  examples.  The 
root  is  divided  into  the  body  or  main  portion ;  the  apex,  or 
terminal  end  of  a  root ;  and  the  neck,  which  marks  the 
junction  of  the  root  with  the  crown.  A  tooth  is  also  marked 
with  a  slight  constriction  at  the  neck,  and  by  the  junction 
of  the  enamel  with  the  cementum.  The  latter,  which  forms  a 
visible  line  encircling  the. tooth,  is  called  the  gingival  line. 
It  is  so  curved  in  its  course  as  to  present  a  convexity  toward 
the  crown  on  the  proximate  surfaces,  to  correspond  with  the 
line  of  the  gum  as  it  passes  over  the  alveolar  ridge  from  the 
labial  to  the  lingual  side  of  the  arch.  On  the  anterior  teeth, 
it  is  also  so  curved  in  passing  the  labial  and  lingual  surfaces 
:as  to  present  a  concavity  toward  the  crown.  These  are  called 
the  curvatures  of  the  gingival  line,  or  the  gingival  curvature. 
The  neck  of  a  tooth  is  common  to  all  of  the  roots,  whatever 
the  number,  for  the  point  of  division  into  two  or  more  roots 
is  always  rootward  from  the  neck. 

4.  The  crowns  of  the  incisors  and  cuspids  present  for 
■examination  four  surfaces  and  an  edge ;  and  the  crowns  of 
the  bicuspids  and  molars,  five  surfaces.  These  surfaces  are 
named  according  to  their  position  and  use.  Those  of  the  in- 
cisors and  cuspids  presenting  toward  the  lips,  are  called  labial 
surfaces ;  those  of  the  bicuspids  and  molars  presenting  toward 
the  cheek,  buccal  surfaces ;  all  presenting  toward  the  tongue, 
lingual  surfaces,  whether  in  the  upper  or  the  lower  jaw.* 

5.  The  surfaces  of  the  teeth  that  present  toward,  or  lie 
against,  adjoining  teeth  are  called  proximate,  or  proximal, 

*Soine  authors  use  the  term  "  palatine  surfaces  "  for  those  of  the  upper  jaw,  and 
■"lingual  "  for  those  of  the  lower.    This  seems  unnecessary. 


NOMENCLATURE.  9 


surfaces.  The  proximate  surfaces  are  also  more  closely 
defined  by  the  terms  mesial  and  distal.  These  terms  have 
special  reference  to  the  position  of  the  surface  relative  to  the 
central  or  the  median  line  of  the  face.  This  line  is  drawn  along 
the  suture  uniting  the  superior  maxillary  bones,  or  perpendic- 
ularly through  the  centre  of  the  face  and  mouth,  and  passes 
between  the  central  incisors  of  both  the  upper  and  lower  jaws. 
Those  proximate  surfaces  which,  as  they  are  placed  in  the  arch, 
and  following  its  curve^  are  toward  this  median  line,  are  called 
mesial  surfaces  ;  and  those  most  distant  from  this  median 
line  are  called  distal  surfaces.  The  mesial  surfaces  of  the 
central  incisors,  both  upper  and  lower,  proximate  each  other ; 
but  in  all  other  cases  a  mesial  surface  proximates  a  distal. 
Also,  a  distal  surface  always  proximates  a  mesial  surface, 
except  those  of  the  third  molars,  upper  and  lower,  which 
have  no  distal  proximating  teeth. 

6.  The  angles  formed  by  the  junction  of  any  of  these 
surfaces  are  designated  by  combining  the  names  of  the  two 
uniting  surfaces  into  a  compound  word,  using  the  term 
mesio  or  disto  as  a  prefix,  thus :  mesio-buccal,  mesio-ocduding ^ 
disto-lingual  and  disto-labial  angles. 

7.  The  incisors  present  a  cutting  edge  by  the  junction  of 
the  labial  and  lingual  surfaces  along  a  line.  In  the  cuspids, 
this  joining  of  the  surfaces  to  form  an  edge  is  raised  to  a  point 
near  the  center  of  its  length,  forming  a  cusp,  hence  the  term 
"  cuspid,"  a  tooth  with  one  point.  The  cutting  edges  of  the 
incisors,  and  the  grinding  surfaces  of  the  bicuspids  and  molars, 
are  those  which  occlude  with  the  similar  surfaces  of  the  teeth 
of  the  opposing  jaw  when  the  mouth  is  closed,  as  in  the  act 
of  biting  ;  hence  they  are  called  the  occluding  surfaces.  The 
incisors  and  cuspids  of  the  upper  jaw  do  not  occlude  ex- 
actly on  the  cutting  edges  or  cusps,  but  generally  just  back 
of  them ;  though,  for  convenience,  this  term  is  applied  to 
them  as  if  they  did.  The  occluding  surfaces  of  the  bicus- 
pids have  two  cusps,  hence  the  term  bicuspid,  a  tooth  with 


10  NOMENCLATURE. 


two  points  ;  and  the  occluding  surfaces  of  the  molars  have- 
four,  and  sometimes  more. 

8.  A  cusp  is  a  pronounced  elevation,  more  or  less 
pointed,  on  the  surface  of  a  tooth,  but  more  especially  on  the 
occluding  surface.  A  slight  elevation  is  often  called  a  tubercle, 
as  that  frequently  seen  near  the  gingival  margin  of  the  lin- 
gual surface  of  the  upper  incisors.  These  are  generally 
deviations  from  the  typical  forms  of  the  teeth. 

9.  Long-shaped  elevations  on  the  surfaces  of  teeth  are 
called  ridges,  and  are  named  according  to  their  location  or 
form:  as  buccal  ridge,  lingual  ridge,  and  marginal  ridge. 
Those  ridges  which  descend  from  the  cusps  of  the  molars 
and  bicuspids  toward  the  central  part  of  the  occluding  sur- 
faces are  called  triangular  ridges.  They  are  named  after 
the  cusps  to  which  they  belong,  as,  the  triangular  ridge  of 
the  mesio-buccal  cusp  of  the  upper  first  molar,  or  simply, 
mesio-buccal  triangular  ridge.  When  a  buccal  and  a  lingual 
triangular  ridge  join  they  form  a  transverse  ridge.  In  this 
way  they  often  subdivide  the  central  fossa  of  the  lower 
molars  and  form  supplemental  fossse. 

10.  A  generally  rounded  or  angular  depression  on  the 
surface  of  a  tooth  is  called  a  fossa.  Fossse  occur  mostly  on 
the  occluding  surfaces  of  the  molars.  When  a  notable 
depression  is  long-shaped  it  is  called  a  sulcus.  Some  of  these 
pass  entirely  from  mesial  to  distal  through  the  occluding 
surface  of  a  tooth,  as  in  the  bicuspids.  This  term  is  often 
erroneously  applied  to  the  grooves  and  fissures. 

11.  A  shallow,  long-shaped  depression,  in  the  form  of 
a  line,  on  the  surface  of  a  tooth,  is  called  a  groove.  When 
such  a  groove  follows  the  bottom  of  a  sulcus  it  is  said  to  be 
sulcate.  When  such  a  groove  sinks  suddenly  into  the  sub- 
stance of  a  tooth  in  the  form  of  a  fault  it  is  called  a  fissure."'^ 

*  The  words  sulcus,  groove,  and  fissure  are  often  used  as  if  they  were  synonymous 
and  interchangeable,  which  has  given  rise  to  much  confusion.  It  is  necessary  that  the 
distinctions  made  in  their  use  in  dental  anatomy  be  well  understood.  A  groove  is  a  very 
fine  line  in  the  form  of  a  slight,  sharp  depression  on  the  surface  of  the  tooth,  as  repre- 
sented in  section  in  diagram  A,  at  a  in  a  section  cut  at  the  point  where  the  mesial 


NOMENCLATURE.  11 


There  are  two  varieties  of  grooves  in  the  teeth,  differing 
essentially  in  their  nature  and  formation.  One  class  marks 
the  lines  on  which  the  parts  of  the  teeth  first  formed  sepa- 
rately, are  afterward  joined,  and  is  called  the  essential  or 
developmental  grooves,  or  developmental  lines.  In  their 
relation  to  the  development  of  the  enamel,  they  are  of  the 
same  nature,  and  resemble  the  sutures  of  the  bones  of  the 
skull,  which  mark  the  junction  of  the  separately  formed 
plates.  Hence  these  grooves  form  the  key  to  much  of  de- 
scriptive dental  anatomy ;  and,  when  they  can  be  traced,  enable 
the  anatomist  to  unravel  complex  forms,  and  assign  irregu- 
larly formed  teeth  to  the  groups  to  which  they  belong ;  to 
properly  name  their  individual  parts,  and  identify  any 
additional,  accidental,  or  unusual  forms  or  parts  that  may 
have  become  intermingled  in  the  accident  of  a  faulty  forma- 
tion. These  developmental  grooves,  or  lines,  are  subject  to 
fissures,  which  occur  when,  from  any  cause,  there  is  a  failure 
of  perfect  union  of  the  parts,  leaving  a  fault. 

12.  The  other  class  of  grooves  has  no  especial  relation 
to  the  developmental  lines,  and  are  called  supplemental 
grooves.  These  are  aptly  described  as  wrinkles  in  the  enamel, 
which,  in  fact,  many  of  them  are.  But  some  are  so  constant 
in  their  location  and  form  as  to  make  up  a  portion  of  the 
typical   tooth  form.     The  supplemental  grooves  are  usually 

groove  passes  over  the  marginal  ridge  of  a  bicuspid.  Diagram  B,  from  a  section  of  a  bi- 
cuspid, a  cut  across  verj'  close  to  the  occluding  surface  grooves  are  shown  at  a,  a.  A  very- 
shallow  depression  with  rounded  bottom  is  also  called  a  groove,  as  those  seen  on  the  labial 
surfaces  of  the  incisors.  A  sulcate  groove  is  one  that  follows  a  sulcus  of  notable  depth,  the 
inclines  of  which  approach  each  other  at  an  angle,  as  represented  at  a,  in  Diagram  C. 
A  fissure  is  always  a  fault  in  the  enamel,  a  point  where  the  margins  of  the  plates  of 
enamel  fail  to  unite,  as  represented  at  a,  in  diagram  D.  These  are  distinctions  of  im- 
portance, and  there  should  be  no  confusion  in  the  use  of  the  words  by  which  we  distin- 
guish them. 

J         ^         C  ^ 


12  MEASUREMENTS    OF    THE    TEETH. 

shallow,  with  well-rounded  bottoms,  and  are  not  ordinarily 
subject  to  fissure. 

13.  In  the  mesio-distal  direction  all  of  the  teeth  are  a 
little  broader  at  or  near  their  occluding  surfaces  than  at  their 
necks ;  therefore,  as  they  stand  in  the  well-formed  arch,  their 
proximate  surfaces  touch  only  at  or  near  their  occluding  sur- 
faces, leaving  V-shaped  openings  between  their  necks.  These 
are  called  inter-proximate  spaces.  IsTormally,  the  inter- 
proximate  spaces  are  filled  with  gum  tissue. 

14.  The  teeth  of  difterent  individuals  show  considerable 
variety  of  form.  Some  persons  have  teeth  with  very  long 
crowns,  broad  in  the  mesio-distal  direction  at  their  occluding 
surfaces  and  narrow  at  their  necks.  These  present  large 
inter-proximate  spaces.  They  are  known  as  "  bell-crowned  " 
teeth.  Again,  some  individuals  have  teeth  that,  in  their 
mesio-distal  diameter,  are  nearly  as  thick  at  their  necks  as 
at  the  occluding  surfaces,  making  their  inter-proximate 
spaces  very  narrow,  the  teeth  almost,  or  quite,  touching 
along  the  whole  length  of  the  crown.  These  are  known  as 
thick-necked  teeth.  The  more  common  form  is  midway 
between  these  two  extremes.  The  teeth  of  some  individuals 
and  families  have  very  long  cusps ;  those  of  others  have 
very  short  cusps.  Some  are  deeply  marked  by  grooves  and 
sulci,  and  in  those  of  others  the  grooves  and  sulci  are 
shallow.  Thus,  there  is  considerable  variety  of  contour 
without  change  of  type. 

15.  In  the  following  tables  the  results  of  the  measure- 
ment of  many  teeth  of  each  denomination  are  given.  The 
numbers  we  had  of  the  different  varieties  differed,  but  in  all 
denominations  they  were  sufficient  to  insure  reasonable  accu- 
racy as  to  the  average  size.  There  are  three  measurements 
given,  the  average,  greatest,  and  least,  in  the  several  posi- 
tions measured.  With  a  greater  number,  both  larger  and 
smaller  teeth  might  be  found,  so  that  the  tables  must  not 
be  taken  to  represent  the  greatest  nor  the  least  that  might 


MEASUREMENTS    OF    THE    TEETH. 


be  found ;  but  the  occurrence  of  larger,  or  longer  teeth  must 
be  rare. 

The  lines  of  measurement,  are  : 

1st.  "  Length  over  all:"  Length  of  the  tooth  from  the 
cutting  edge,  or  buccal  cusp,  to  the  apex  of  the  root. 

2d.  "Length  of  crown:"  Length  of  the  crown  from 
the  cutting  edge,  or  buccal  cusp,  to  the  gingival  line  on  the 
labial  or  buccal  surface. 

3d.  "  Length  of  root :"  Length  of  root  from  the  gingival 
line  on  the  buccal  surface  to  the  apex  of  the  root. 

4th.  "  Mesio-distal  diameter  6f  crown:"  This  is  the 
extent  from  mesial  to  distal  in  the  greatest  diameter,  or  at 
the  points  of  proximate  contact. 

5th.  "  Mesio-distal  diameter  of  neck  :"  This  measure- 
ment was  made  at  the  gingival  line. 

6th.  "  Labio-  or  bucco-lingual  diameter:"  This  meas- 
urement was  taken  at  the  greatest  diameter  of  the  crown  in 
the  direction  named.  In  the  incisors  it  was  on  the  gingival 
ridge.  In  the  bicuspids  and  molars  it  was  generally  mid. 
length  of  the  crown,  but  occasionally  it  was  near  the  gingival 
line,  especially  in  the  upper  second  and  third  molars. 

7th.  "  Curvature  of  the  gingival  line :"  This  is  the 
height  or  extent  of  the  curve  of  the  gingival  line  toward  the 
cutting  edge,  or  occluding  surface,  as  it  passes  from  labial  to 
lingual,  measured  on  the  mesial  surface. 

Having  these  tables,  the  necessity  for  giving  many 
measurements  in  the  text  is  avoided. 


14 


MEASUREMENTS   OF   THE   TEETH. 


Table  of  Measurements  of 
THE  Teeth  of  Man,  Given 
IN  Millimeters  and 
Tenths  of  Milli- 
meters.* 

22.5 
27.0 
18.0 

o 

t-l 
o 

o 
a 

o 
o 

ft 

0 
a 

.—  0 

TS    0 

is 

1    si 

0    CD 
0  ■♦^ 
0    <» 

=  a 

31 

s  > 

0 

UPPER  TEETH. 

'nisor      ^-S: 

Incisor.             Least. 

10.0 
12.0 

8.0 

12.0 

16.0 

8.0 

9.0 
10.0 

8.0 

6.3 

7.0 
5.5 

7.0 
8.0 
7.0 

3.0 
4.0 

2.0 

Lateral                     GleaSt' 

22.0 
26.0 
17.0 

8.8 

10.5 

8.0 

13.0 

16.0 

8.0 

6.4 
7.0 
5.0 

4.4 
5.0 
4.0 

6.0 
7.0 
5.0 

2.8 
4.0 
2.0 

Average. 
Cuspid.                    Greatest. 
Least. 

26.5 
32.0 
20.0 

9.5 

12.0 

8.0 

17.3 
20.5 
11.0 

7.6 
9.0 

7.0 

5.2 
6.0 
4.0 

8.0 
9.0 
7.0 

2.5 
3.5 
1.0 

First                         Average. 
■R5„..c,.j^           Greatest. 
Bicuspid.          Least. 

20.6 
22.5 
17.0 

8.2 
9.0 
7.0 

12.4 
14,0 
10.0 

7.2 
8.0 
7.0 

4.9 
6.0 
4.0 

9.1 
10.0 

8.0 

1.1 
2.0 
0.0 

^^«<^°4        .,           Greatest 
Bicuspid.          Least. 

21.5 
27.0 
16.0 

7.5 
9.0 

7.0 

14.0 
19.0 
10.0 

6.8 
8.0 
6.0 

5.3 
6.5 
4.5 

8.8 
10.0 

7.5 

0.8 
1.5 
0.0 

First                         Average. 

20.8 
24.0 
17.0 

20.0 
24.0 
16.0 

17.1 
22.0 
14.0 

7.7 
9.0 
7.0 

13.2 
16.0 
10.0 

10.7 

12.0 

9.0 

7.5 
8.0 
7.0 

11.8 
12.0 
11.0 

2.2 
3.0 
1.0 

Second                     ATerage. 
Molar.              SSr- 

7.2 
8.0 
6.0 

6.3 
8.0 
5.0 

13.0 

17.0 

9.0 

9.2 

10.0 
7.0 

6.7 
8.0 
6.0 

11.5 
12.5 
10.0 

1.6 
4.0 
0.0 

Third                        Average. 

11.4 

15.0 

8.0 

8.6 

11.0 

7.0 

6.1 
8.0 
5.0 

10.6 

14.5 

8.0 

0.7 
2.5 
0.0 

*T]iere  are  25.4  millimeters  to  the  inch. 


MEASUREMENTS   OF   THE   TEETH. 


15 


Table  of  Measurements  of 
THE  Teeth  of  Man,  Given 
IN  Millimeters  and 
Tenths  op  Milli- 
meters. 

'3 

u 

0) 

> 
o 

fl 

0) 

2 

o 
o 

to 
a 
<u 

o 
o 

o 

C 

3  2 
.2  ^ 

^  a 

,  13 

.2  S3 

8  « 

O  r^S 

^1 

0) 

^  s 

>  a 

g"3o 

o 

LOWER  TEETH. 

Central  _                    aleaSt 
I^"««^-             Least. 

20.7 
24.0 
16.0 

21.1 

27.0 
18.0 

8.8 

10.5 

7.0 

11.8 

16.0 

9.0 

5.4 
6.0 
5.0 

3.5 
5.0 
2.5 

6.0 
6.5 
5.5 

2.5 
3.0 
1.5 

Lateral                    ^J^f^e. 
Incisor.             Greatest. 
Least. 

9.6 
12.0 

7.0 

12.7 
17.0 
11.0 

5.9 
6.5 
5.0 

3.8 
50 
3.0 

6.4 
7.5 
6.0 

2.5 
3.5 
2.0 

Average. 
Cuspid.                     Greatest. 
Least. 

25.6 
32.5 
20.0 

10.3 
12.0 

8.0 

15.3 
21.0 
11.0 

6.9 
9.0 
5.0 

52 
7.0 
3.0 

7.9 

10.0 

6.0 

2.9 
4.0 
2.0 

First                         Average. 

!?•„       -A           Greatest. 
Bicuspid.          j^^^^^ 

21.6 
26.0 
18.0 

7.8 
9.0 
6.5 

14.0 
18.0 
11.0 

6.9 
8.0 
6.0 

4.7 
5.0 
4.5 

7.7 
8.0 
7.0 

0.8 
1.5 
0.5 

Second                     ^I^ejfgJ- 

22.3 
26.0 
18.0 

21.0 
24.0 
18.0 

7.9 

10.0 

6.0 

14.4 
17.5 
11.5 

7.1 

8.0 
6.5 

4.8 
6.5 
4.0 

8.0 
9.0 
7.0 

0.6 
2.0 
0.0 

First                        ^-"^'fSe- 
M«^-               Sir- 

7.7 

10.0 

7.0 

13.2 
15.0 
11.0 

11.2 
12.0 
11.0 

8.5 
9.5 

7.5 

10.3 
11.5 
10.0 

1.1 
2.0 
0.0 

Second                     Average. 

19.8 
22.0 
18.0 

6.9 
8.0 
6.0 

12.9 
14.0 
12.0 

10.7 
11.0 
10.0 

8.1 

8.5 
8.0 

10.1 

10.5 

9.5 

0.2 
1.0 
0.0 

Third                       Average. 
Molar.              g^r- 

18.5 
20.0 
16.0 

6.7 
8.0 
6.0 

11.8 

17.0 
8.0 

10.7 

12.0 

8.0 

8.3 
9.5 
5.0 

9.8 

10.5 

9.0 

0.2 
1.5 
0.0 

16 


MEASUREMENTS    OF    THE   TEETH. 


Table  of  Measurements  op 
THE  Deciduous  Teeth  of 
Man,  Given  in  Milli- 
meters and  tenths 
of  Millimeters. 

> 
o 

to 

c 
16.0 

& 
o 
u 

c 

o 
to 

§ 

u 
o 

a 

rO     O 
6     fH 

-J 
^  o 

.s 

a 

.^  o 
.2S 

pt4 

.S  ° 

Averages  Only. 

11 

UPPEE  TEETH. 

T3 

Central  Incisor. 

6.0 

10.0 

6.5 

4.5 

5.0 

4.0 

Lateral  Incisor. 

15.8 
19.0 

5.6 

6.5 

11.4 

5.1 

3.7 

4.8 

3.7 

Cuspid. 

13.5 

7.0 

5.1 

7.0 

5.5 

First  Molar. 

15.2 

5.1 

10.0 

7.3 

5.2 

8.5 

6.9 

Second  Molar. 

17.5 
14.0 

5.7 
5.0 

11.7 
9.0 

8.2 
4.2 

6.4 
3.0 

10.0 
4.0 

8.3 

LOWER  TEETH. 

Central  Incisors. 

3.5 

Lateral  Incisors. 

15.0 
17.0 

5.2 
6.0 

10.0 

4.1 

3.0 

4.0 

3.5 

Cuspids. 

11.5 

5.0 

3.7 

4.8 

4.0 

First  Molar. 

15.8 

6.0 

9.8 

7.7 

6.5 

7.0 

5.3 

Second  Molar. 

18.8 

5.5 

11.3 

9.9 

7.2 

8.7 

6.4 

MEASUREMENTS    OF   THE   TEETH. 


17 


Table  of  Measurements  of 

THE   Teeth    of   Man;    in 

Inches  and  Hundredths 

OF  an  Inch. 

1 
1 

"^ 
u 

> 

o 
bb 

a 

p 
3 
o 

,5 

"so 
a 
<a 

1-1 

0 
2 

Cm 
0 

"Si 

a 

-3  2 

n3  0 

.2  33 

tn  -is 

03 

^4 
03  a> 

T3    0 

03 

8-2 

.21 

c3  a 

-^  a 

0 

UPPER  TEETH. 

Central.                   ^JS: 
I°^^^«^-             Least. 

.88 
1.06 

.72 

.39 
.41 
.31 

.49 
.63 
.31 

.35 
.39 
.31 

.24 
.27 
.21 

.27 
.31 

.27 

.11 

,15 

.07 

^ntisor              ^-S- 
^^«^^«^-             Least. 

.86 

1.02 

.66 

.34 
.41 
.31 

.51 
.63 
.31 

.25 
.27 
.19 

.17 
.19 
.15 

.23 
.23 
.19 

.11 
.15 

.07 

Average. 
Cuspid.                     Greatest. 
Least. 

1.04 

1.26 

.79 

.37 
.47 
.31 

.68 
.80 
.43 

.29 
.35 

.27 

.20 
.23 
.15 

.31 
.35 

.27 

.09 
.13 
.03 

First                         Average. 

"bicuspid,   sr 

.81 
.89 
.66 

.32 

.35 

.27 

.48 
.55 
.39 

.28 
.31 

.27 

.19 
.23 
.15 

.35 
.39 
.31 

.04 
.07 
.00 

.84 

1.06 

.62 

.29 

.29 

.27 

.55 
.55 
.39 

.26 
.31 
.23 

.20 
.25 
.17 

.34 
.39 

.29 

.03 

.05 
.00 

First                          Average. 

.81 
.94 
.66 

.30 
.35 

.27 

.51 
.62 
.39 

.42 
.47 
.35 

.29 
.31 

.27 

.46 
.47 
.43 

.08 
.11 
.03 

ijeast. 

.78 
.94 
.62 

.28 
.31 
.23 

.51 
.66 
.35 

.36 
.39 

.27 

.26 
.31 
.23 

.45 
.49 
.39 

.05 
.15 
.00 

Third                       Average. 
Molar.               Greatest. 
Least. 

.67 
.86 
.55 

.24 
.31 
.19 

.44 
.59 
.81 

.33 
.43 

1  .27 

.23      .41 
.31      .57 
.19      .31 

.02 
.09 
.00 

18 


MEASUREMENTS    OF   THE    TEETH. 


Table  of  Mt^iasurements  of 

THE    Teeth    of    Man;    in 

Inches  and  Hundredths 

OF  AN  Inch. 

Is 
u 

> 
o 

bo 

g 

o 
o 

"So 

a 

1-1 

o 
o 

u 

1-1 

3  2 

13    O 

O    Si 

^4 

o  u 

II 

6  S3 

.si 

<u 

LOWER  TEETH. 

^     ,     1                     Average. 
<^«^tfl.                   Greatest. 
Incisor.             Least. 

.80 
.94 
.63 

.34 
.41 

.27 

.47 
.62 
.35 

.22 
.23 
.19 

.13 
.19 
.09 

.23 
.26 
.21 

.09 
.11 
.05 

Average. 
Lateral                     Greatest. 
Incisor.             Least. 

.83 
1.06 

.70 

.35 
.46 
.27 

.50 
.66 
.43 

.23 
.26 
.19 

.15 
.19 
.11 

.25 
.29 
.25 

.09 
.13 

.08 

Average. 
Cuspid.                    Greatest. 

Least. 

1.01 
1.28 

.78 

.40 
.46 
.32 

.60 
.82 
.43 

.27 
.35 
.23 

.20 

.27 
.11 

.31 
.39 
.24 

.11 
.14 
.08 

T-,-    ^                          Average. 
-RVn«.lH            Greatest. 
Bicuspid.          Least. 

.84 

1.02 

.71 

.30 
.35 
.25 

.54 
.70 
.43 

.27 
.32 
.23 

.18 
.20 
.16 

.30 
.31 

.27 

.03 
.05 
.01 

j:,         j                      Average. 

^'°^1.«.;^           Greatest. 
Bicuspid.           Least. 

.87 

1.02 

.71 

.31 
.43 
.23 

.56 
.63 

.45 

.28 
.32 
.25 

.18 
.25 
.15 

.31 
.35 

.27 

.02 
.07 
.00 

First                          Average. 
TVT  1                    Greatest. 
M°l^^-              Least. 

.78 
.94 
.71 

.30 
.39 

.27 

.52 
.59 
.43 

.33 
.37 
.23 

.33 
.37 
.29 

.40 
.45 
.39 

.04 
.07 
.00 

Second                     ^!ffS- 

Molar.     s::r 

.78 
.86 
.71 

.27 
.31 
.23 

.50 
.55 
.47 

.42 
.43 
.39 

.32 
.33 
.31 

.39 
.41 
.37 

.00 
.00 
.00 

Tl^-t  ,                  G3st 
Molar.              Least. 

.72 
.78 
.63 

.26 
.32 
.23 

.36 
.66 
.31 

.42 
.47 
.31 

.32 
.37 
.20 

.38 
.41 
.35 

.00 
.04 
.00 

UPPER   CENTRAL   INCISORS. 


19 


Table  of  Measukements  of 

THE    DECTDrOUS    TeETH    OF 

Man,   Given   in   Inches 

and   hundeedths   of 

AN  Inch. 

Averages  Only. 
UPPER  TEETH. 


Lateral  Incisor. 


Cuspid. 


s 

& 

o 

o 

u 

p 

<0 

o 

> 

«M 

>u 

o 

O 

o 

^ 

^ 

^ 

60 

60 

60 

c 

S 

c 

<a 

<u 

a> 

^ 

1-1 

H-1 

Central  Incisor. 

.63 

.23 

.39 

.25 

.18 

.20 

.16 

Lateral  Incisor. 

.62 

.25 

.45 

.20 

.14 

.19 

.14 

Cuspid. 

.74 

.25 

.53 

.27 

.20 

.27 

.21. 

First  Molar. 

.59 

.20 

.39 

.28 

.20 

.33 

.27 

Second  Molar. 

.68 
.55 

.22 
.19 

.46 
.35 

.32 
.15 

.25 
.11 

.39 
.15 

.32 

LOWER  TEETH. 

Central  Incisor. 

.13 

First  Molar. 


.59  j  .19  i  .39  I  .15  I  .11  j  .15  |  .13 
'm~\  .23  I  .45  I  .19  I  .14  I  .17  |  .15 
'!62~|  .24  I  .38  I  .30  I  .25  |  .27  I  .21 


Second  Molar. 


.62     .21 


.44     .38      .28      .34     .25 


UPPER   CENTRAL   INCISORS." 

16.  The  right  and  left  upper  central  incisors  are  sit- 
uated in  the  extreme  anterior  part  of  the  dental  arch,  one 
on  each  side  of  the  raedian  line,  their  mesial  surfaces  proxi- 
mating  each  other.  The  crown  presents  four  surfaces  (five, 
including  the  cutting  edge),  four  angles,  and  a  cutting  edge, 
or  occluding  surface.  The  general  contour  of  the  crown  is 
similar  to  a  wedge,  with  rounded  angles  and  merging  into  a 
rounded  form  at  the  thick  end,  or  the  neck  of  the  tooth.     It 


*  U<^allv  ill  the  descriptions  of  the  teeth,  those  of  one  side  oulv  will  be  mentioned 
^rithout  reference  to  which  side  in  the  text.  Accompanying  the  illustrations  the  side 
to  wMrfithlt(Mth  belongs  will  be  given.  The  student  wiU  readily  determine  to  which 
sfdlaliTefeTinple  belongs  by  comparing  it  ^vith  the  text  and  correctly  naming  its 

surfaces. 


20  UPPER   CENTRAL   INCISORS. 

is  slightly  bent  on  its  shorter  diameter,  so  as  to  make  the 
flattened  labial  surfaces  convex ;  while  the  other,  the  lingual, 
is  concave.  The  crown  is  also  slightly  bent  in  the  mesio- 
distal  direction,  so  that  the  labial  surface  is  convex  and  the 
lingual  concave  in  this  direction.  Therefore,  there  is  a  general 
convexity  of  the  labial,  and  a  general  concavity  of  the 
lingual  surface. 

17.  The  labial  surface  of  the  crown  of  the  upper  central 
incisor  (Fig.  1),  in  its  general  form,  is  an  imperfect  square, 
with  its  gingival  side  rounded.  The  mesial  margin  is  a  little 
longer  than  the  distal,  so  that  the  cutting  edge  slopes  away 
toward  the  distal  angle  (Fig.  1,  A).  Both  the  angles, 
formed  by  the  proximate  surfaces  and  cutting  edge,  are 
slightly  rounded,  the  distal  more  than  the  mesial,  after 
which  the  proximate  surfaces  converge  toward  the  long  axis 
of  the  tooth,  making  the  crown  a  little  narrower  at  the  neck 
than  at  the  cutting  edge. 

18. .  The  lingual  surface  of  the  crown  (Fig.  2)  is  con- 
cave in  all  directions,  forming  a  fossa,  bounded  by  the  cutting 
edge  (a),  the  mesial  and  distal  marginal  ridges  {n,  m)  and 
the  gingival  ridge,  or  cingulum  [d).  The  marginal  ridges 
are  strong  elevations  of  the  enamel,  running  from  the  mesial 
and  distal  angles  of  the  cutting  edge  along  the  borders  of 
this  surface  to  near  the  gingival  line,  where  they  join  the 
gingival  ridge.  The  gingival  ridge  is  a  strong  elevation  of 
the  enamel  forming  the  lingo-gingival  border  of  the  crown, 
sometimes  elevated  into  a  tubercle.  The  lingual  fossa  is 
usually  smooth,  and  the  ridges  by  which  it  is  bounded  are  not 
prominent.  In  many  instances,  however,  there  is  a  deep  pit 
at  the  junction  of  the  gingival  ridge  with  the  lingual  surface 
proper ;  and  in  some  a  groove  extends  from  the  pit  for  a 
short  distance  along  the  border  of  each  marginal  ridge 
(Fig.  3).  These  latter  may,  or  may  not,  be  fissured.  In  a 
few  examples  the  enamel  of  this  surface  has  irregular 
wrinkles,  or  ridges  and  grooves,  running  from  the  gingival 


Fig.  4. 


Fig.  5. 


Fig.  1*  (Par.  17).— Right  Upper  Central  Incisor,  Labial  Surface,  a,  Cutting 
edge ;  6,  mesial  surface ;  c,  distal  surface ;  d,  labial  surface ;  e,  e,  labial  grooves ;  g, 
mesial  angle ;  h,  distal  angle ;  i,  body  of  root ;  k,  apes  of  root. 

Fig.  2*  (Par.  18).— Right  Upper  Central  Incisor,  Lingual  Surface,  a,  Cutting 
edge ;  b,  mesial  surface ;  c,  distal  surface ;  d,  gingival  ridge,  or  cingulum ;  g,  mesial 
angle ;  h,  distal  angle ;  i,  body  of  root ;  k,  apex  of  root ;  m,  distal  marginal  ridge ;  n, 
mesial  marginal  ridge. 

Fig.  3  *  (Par.  18).— Left  Upper  Central  Incisor,  Lingual  Surface,  showing  lingual 
pit.  The  cutting  edge,  a,  is  considerably  worn.  The  mesial  and  distal  marginal  ridges, 
6,  c,  are  prominent ;  d,  linguo-gingival  ridge ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal 
angle ;  i,  body  of  root ;  k,  apex  of  root ;  m,  lingual  pit. 

Fig.  4*  (Par.  19).— Right  Upper  Central  Incisor,  Mesial  Surface,  a,  Mesial  angle ; 
d,  gingival  ridge ;  /,  /,  gingival  line,  showing  its  labio-lingual  curvature ;  i,  body  of 
root ;  k,  apex  of  root. 

Fig.  5*  (Par.  21).— Left  Upper  Central  Incisoe,  Lingual  Surface.  Young,  un- 
worn tooth.  The  developmental  lines,  or  grooves,  are  made  diagrammatically  promi- 
nent to  show  the  form  of  the  lobes,  a,  Middle  lobe ;  b,  mesial  lobe ;  c  distal  lobe ;  d, 
lingual  lobe ;  e,  e,  linguo-gingival  groove ;  /,  /,  Ungual  developmental  grooves ;  g,  mesial 
angle ;  ft,  distal  angle. 

*  Illustration,  1}4  diameters. 


UPPER    CENTRAL   INCISORS.  23 

ridge  toward  the  cutting  edge.     In  malformed  teeth  this 
surface  is  often  very  imperfect. 

19.  The  mesial  and  distal  surfaces  each  present  the 
outline  of  the  letter  Y,  with  its  lines  curved  with  the  con- 
vexity toward  the  lips,  and  the  acute  angle  at  the  cutting 
edge  (Fig.  4).  The  mesial  surface  is  almost  straight  from 
the  angle  of  the  cutting  edge  to  the  gingival  line.  It  is 
convex  from  labial  to  lingual,  hut  nearly  flat  toward  the 
gingival  line;  while  in  some  there  is  even  a  slight  concavity, 
centrally  at,  or  near,  the  gingival  line.  In  the  labio-lingual 
direction,  the  distal  surface  is  rounded,  as  in  the  mesial.  In 
the  majority  of  examples  it  is  also  convex  in  the  direction 
of  the  long  axis  of  the  tooth,  so  that  it  bellies  out  toward 
the  lateral  incisor. 

20.  At  the  gingival  line,  the  tooth  is  a  little  constricted, 
forming  a  slight  furrow;  or  rather,  the  root  at  the  neck  is 
a  little  smaller  than  the  crown,  and  the  enamel  slopes  down 
to  the  size  of  the  root,  giving  the  appearance  of  a  continuous 
ridge  of  enamel  around  the  neck  of  the  tooth.  This  line 
does  not  run  horizontally  around  the  neck  of  the  tooth.  On 
the  proximate  side  it  forms  a  curve  with  the  convexity 
toward  the  crown,  and  on  the  labial  and  lingual  surfaces  it 
forms  a  curve  with  the  concavity  toward  the  crown.  This 
line  marks  the  limit  of  the  attachment  of  the  peridental 
membrane  to  the  root  of  the  tooth. 

21.  Developmental  lines  (Fig.  5).  "When  any  of  the 
incisors  first  appear  through  the  gums  there  are  three  little 
eminences,  or  tubercles,  on  the  cutting  edge  with  grooves 
crossing  from  labial  to  lingual  between  them  {a,g,h).  These 
grooves  run  some  distance  on  the  labial  surface,  becoming 
broader  and  shallower  till  they  disappear.  In  many,  these 
lines  appear  on  the  lingual  surface  between  the  marginal  ridges 
and  the  fossa  (/,/).  Occasionally,  they  are  seen  as  far  as  the 
gingival  ridge.  The  little  tubercles  are  soon  removed  from 
the  edge  by  wear,  leaving  it  straight,  or  slightly  curved. 


24  UPPER   CENTRAL   INCISORS. 


These  lines  divide  this  part  of  the  crown  of  the  tooth  into 
three  labial  lobes.  Calcification  begins  in  these  tubercles  as 
separate  pieces,  or  plates,  and  the  grooves  are  the  marks  of  the 
after-confluence  of  these  plates.  This  is  common  to  the  inci- 
sors and  cuspids.  These  teeth  are  sometimes  fissured  across  the 
cutting  edge,  marking  an  imperfect  confluence  of  the  primary 
plates.  The  calcification  of  the  gingival  ridge,  or  cingulum,  is 
also  begun  as  a  separate  plate,  forming  the  lingual  lobe,  but 
afterward  it  becomes  united  to  the  other  parts  by  confluence, 
leaving  a  groove,  often  very  slight,  indeed,  and  soon  obliter- 
ated by  wear,  marking  the  line  of  union.  This  is  the  linguo- 
gingival  groove  {e,  e).  In  smooth  regularly  formed  teeth  it 
begins  at  the  gingival  line  just  distal  to  the  summit  of  its 
labio-lingual  curvature,  and  runs  across  the  marginal  ridge  at 
right  angles  with  its  length,  then  runs  almost  horizontally 
across  the  lingual  surface  to  the  distal  marginal  ridge.  This 
ridge  is  now  crossed  at  right  angles,  and  the  gingival  line 
reached.  The  length  of  the  groove  usually  includes  from  a 
quarter  to  a  third  of  the  circumference  of  the  tooth.  When 
the  gingival  ridge  is  prominent,  or  rises  in  the  form  of  a 
tubercle,  this  groove  is  subject  to  much  variation  in  its 
course.  Often,  there  is  a  deep  pit  in  the  center  of  its  length ; 
«.e.,  centrally  in  the  lingual  surface,  at  the  margin  of  the 
gingival  ridge  (Fig.  3,  m).  From  this,  fissures  may  extend 
laterally.  Occasionally,  especially  in  the  lateral  incisors,  a 
sulcus,  or  a  fissure  divides  the  gingival  ridge  from  one  of  the 
marginal  ridges,  and  extends  into  the*cementum.  This  is 
the  gingival  fissure. 

22.  The  root  of  the  upper  central  incisor  (Figs,  1  to  5) 
is  about  one  and  a  fourth,  to  one  and  a  half  times  as  long  as 
the  crown.  It  is  conical  in  form,  tapering  from  the  crown 
to  the  apex ;  less  rapidly  near  the  neck,  and  more  rapidly  as 
the  apex  is  approached.  Therefore,  the  body  of  the  root 
seems  a  little  swollen.  However,  the  root  of  this  tooth 
presents  great  variety  of  figure,  as  do  the  roots  of  teeth 


Fig.  6. 


Fig.  8. 


Fig.  10. 


Fig.  6*  (Par.  24).— Right  Upper  Lateral  iNasoR,  Labial  Surface,  a,  Cutting 
edge ;  c,  distal  surface ;  e,  labial  grooves ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal 
angle. 

Fig.  7  *  (Par.  25).— Right  Upper  Lateral  Incisor,  Mesial  Surface,  a,  Mesial  angle ; 
d,  linguo-gingival  ridge ;  /,/,  gingival  line ;  i,  body  of  root ;  fc,  apex  of  root. 

Fig.  8*  (Par.  26).— Right  Upper  Lateral  Incisor,  Lingual  Surface,  without  lingual 
pit.  a,  Cutting  edge ;  6,  mesial  marginal  ridge  ;  c,  distal  marginal  ridge ;  /,  gingival  line ; 
g,  mesial  angle ;  h,  distal  angle ;  i,  body  of  root ;  k,  apex  of  root ;  m,  lingual  fossa. 

Fig.  9  *  (Par.  26).— Right  Upper  Lateral  Incisor,  Lingual  Surface,  with  lingual 
pit.  o.  Cutting  edge ;  6,  mesial  marginal  ridge ;  c,  distal  marginal  ridge  with  linguo- 
gingival  groove  crossing  it ;  d,  linguo-gingival  ridge,  or  eingulum ;  /,  gingival  line  ;  g, 
mesial  angle  ;  h,  distal  angle  ;  i,  body  of  root ;  k,  apes  of  root ;  m,  lingual  pit. 

Fig.  10*  (Par.  26).— Right  Upper  Lateral  Incisor,  showing  a  linguo-gingival  fissure. 
a.  Cutting  edge ;  &,  linguo-gingival  groove ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal 
angle. 

Fig.  11*  (Par.  27).— Upper  Lateral  Incisor,  Mesial  Surface.  Very  short  root,  a. 
Mesial  angle ;  d,  linguo-gingival  ridge ;  /,  gingival  line. 


*  Illustration,  IJ^  diameters. 


UPPER   LATERAL   INCISOR.  27 


generally.  The  root  is  nearly  round  at  the  neck.  The  cur- 
vature of  the  Ungual  surface  is  the  arc  of  a  smaller  circle 
than  that  of  the  labial.  The  proximate  surfaces  are  slightly 
flattened.  The  flattened  portion  of  the  mesial  surface  is  a 
little  broader  than  the  distal.  These  two  converg-e  to  the 
lingual,  giving  the  form  of  a  prism  with  its  angles  rounded. 

UPPER   LATERAL   INCISOR. 

23.  The  description  of  the  lateral  incisor  may  be  much 
abridged,  because  of  its  resemblance  to  the  central  in  its  general 
form  and  developmental  lines.  The  tooth  is  a  little  shorter, 
and  from  mesial  to  distal  the  crown  is  about  a  third  narrower. 

24.  The  labial  surface  of  the  lateral  incisor  (Fig.  6)  is 
more  rounded  in  the  mesio-distal  direction  than  in  the  cen- 
tral. The  mesial  angle  is  acute,  and  the  cutting  edge  slopes 
away  in  a  curve  to  a  rounded  and  obtuse  distal  angle.  The 
cutting  edge,  at  the  time  of  eruption,  presents  three  tubercles, 
and  the  grooves  crossing  the  edge  between  these  are  projected 
on  the  labial  surface  as  shallow  labial  grooves. 

25.  The  mesial  (Fig.  7)  and  distal  surfaces  present  the 
characteristic  V-shape  of  all  the  incisors.  From  labial  to 
lingual  the  mesial  surface  is  rounded  near  the  cutting  edge, 
but  much  flattened  near  the  gingival  line.  Sometimes  a 
slight  concavity  exists  at  this  point.  Occasionally  the  mesio- 
labial  angle  has  a  flattened  or  sunken  point  of  enamel  near 
the  middle  of  its  length.  This  is  sometimes  broad  and  of 
notable  depth,  and  in  this  case  is  generally  in  the  labial 
portion  of  the  mesial  surface.  In  others,  it  is  a  small  im- 
perfection in  the  mesial  border  of  the  labial  surface.  The 
distal  surface  is  convex  in  all  directions.  In  its  occlusive 
third,  it  rounds  out  freely  toward  the  cuspid,  but  becomes 
more  flattened  toward  the  gingival  line. 

26.  The  lingual  surface  (Fig.  8)  of  lateral  incisors,  is 
very  irregular  in  the  extent  of  its  concavity.  Some  are 
almost  flat,  while  others  are  deeply  concave.      The  mesial 


28  THE   LOWER   INCISOES. 


and  distal  marginal  ridges  are  proportionately  broader,  and 
stronger,  than  in  the  centrals.  In  the  majority  of  examples 
the  lingual  surface  is  the  broadest  part  of  the  crown.  The 
rounding  of  the  proximate  surfaces  is  at  the  expense  of  the 
labial  surface,  so  that  a  moderately  acute  angle  is  formed  by 
the  junction  of  the  proximate  surfaces  with  the  lingual. 
Generally,  the  lingual  surface  is  almost  smooth,  but  in  many, 
a  pit,  with  or  without  lateral  fissures,  will  be  found  at  the 
junction  of  the  lingual  surface  proper,  with  the  gingival 
ridge  (Fig.  9).  In  some  of  these,  the  gingival  ridge  is 
unusually  short,  so  that  the  marginal  ridges  are  folded  in 
together  at  their  gingival  ends,  forming  a  deep  sulcus  be- 
tween them,  and  there  is  a  deep  pit  at  their  junction.  Again, 
some  are  found  in  which  there  is  a  deep  groove,  which  is 
often  fissured,  dividing  one  marginal  ridge  from  the  gingival 
ridge,  and  extending  into  the  cementum  (Fig.  10).  This  is  some- 
times nearly  central,  giving  the  appearance  of  a  failure  of  the 
lingual  lobe,  or  of  a  division  of  the  lobe  centrally,  or  of  the  dis- 
placement of  the  lobe  to  one  side.    This  is  the  gingival  fissure. 

27.  The  root  of  the  upper  lateral  incisor  (Figs.  6  to  11) 
is  conical,  but  considerably  flattened  on  its  mesial  and  distal 
sides,  which  is  generally  maintained  to  the  apex.  The  root 
is  generally  straight,  and  about  one  and  a  half  times  as  long 
as  the  crown.  In  many  specimens  the  apex  is  curved  to  the 
distal.     Occasionally  the  root  is  very  crooked. 

28.  The  ujDper  lateral  incisor  presents  much  variety  of 
size  and  form.  It  is  not  uncommon  to  find  narrow  laterals 
associated  with  broad  centrals.  The  lateral  incisors  are 
more  often  imperfectly  developed  than  the  other  anterior 
teeth.  In  these,  the  crown  of  the  tooth  is  frequently  conical, 
with  a  rounded,  or  even  a  moderately  sharp,  point. 

THE   LOWER   INCISORS. 

29.  The  lower  incisors  have  outlines  similar  to  the 
upper  lateral,  but  are,  in  every  way,  more  slender.     Their 


Fig.  12. 


Fig.  15. 


Fig.  17. 


Fig.  12*  (Par.  29).— Left  Lower  Central  Incisor,  Labial  Surface.  Long  root. 
a,  Cutting  edge ;  e,  labial  grooves ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal  angle. 

Fig.  13*  (Par.  29).— Left  Lower  Lateral  Incisor,  Labial  Surface.  Long  root. 
a,  Cutting  edge ;  e,  labial  grooves ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal  angle ;  i, 
body  of  root ;  k,  apex  of  root. 

Fig.  14*  (Par.  29).— Right  Lower  Lateral  Incisor,  Labial  Surface.  Short  root. 
a,  Cutting  edge ;  e,  labial  grooves ;  /,  gingival  line ;  g,  mesial  angle  ;  A,  distal  angle ;  i, 
body  of  root ;  k,  apex  of  root. 

Fig.  15  *  (Par.  30).— Lower  Central  Incisor,  Lingual  Surface,  a,  Cutting  edge ; 
6,  mesial  marginal  ridge  ;  c,  distal  marginal  ridge ;  d,  linguo-gingival  ridge ;  g,  mesial 
angle  ;  h,  distal  angle  ;  m,  lingual  ridge. 

Fig.  16  *  (Par.  30).— Lower  Central  Incisor,  Distal  Surface.  a,  Cutting  edge ; 
the  edge  is  worn  away  as  represented  by  the  line ;  d,  linguo-gingival  ridge ;  /,/,  gingival 
line  ;  i,  groove  along  the  distal  side  of  root ;  k,  apex  of  root. 

Fig.  17  *  (Par.  31).— Right  Lower  Lateral  Incisor,  Distal  Surface,  showing  root 
deeply  grooved,  a,  Cutting  edge  ;  d,  linguo-gingival  ridge  ;  /,  gingival  hue  ;  i,  deep- 
groove  in  root ;  k,  apex  of  root. 


*  Illustration,  l}i  diameters. 


THE    LOWER   INCISORS.  31 

developmental  lines  are  the  same,  but  the  grooves  are  much 
less  marked,  and  generally  cannot  be  seen  except  in  unworn 
teeth.  The  cutting  edge  of  the  lower  central  (Fig.  12)  is 
very  nearly  at  right  angles  with  the  long  axis  of  the  tooth, 
and  its  angles  are  square  and  sharp.  From  mesial  to  distal, 
the  cutting  edge  is  the  widest  part  of  the  crown,  and  from  it 
the  proximate  surfaces  converge  equally  to  the  gingival  line, 
reducing  the  mesio-distal  diameter  about  a  third.  The 
lower  lateral  differs  from  the  central  by  the  cutting  edge 
sloping  away  to  the  distal,  the  mesial  angle  being  acute,  and 
the  distal,  obtuse  and  rounded.  The  distal  surface  is  also 
convex  from  the  angle  to  the  gingival  line,  bellying  out 
toward  the  cuspid. 

30.  The  lingual  surface  (Fig  15)  of  the  lower  incisors 
is  concave  from  the  cutting  edge  to  the  gingival  ridge,  over 
which  there  is  a  convexity  (Fig.  16).  l^ear  the  cutting 
edge  this  surface  is  generally  nearly  flat  in  the  mesio-distal 
direction,  but  is  sometimes  concave  or  slightly  convex ;  it 
becomes  convex  progressively  toward  the  gingival  ridge.  In 
many  there  is  a  slight  ridge  on  the  center  of  this  surface  with 
a  shallow  concavity  on  either  side,  which  marks  the  junction 
of  the  lobes,  running  from  near  the  cutting  edge  to  the 
gingival  ridge  (Fig.  15).  The  mesial  and  distal  surfaces  are 
convex  near  the  cutting  edges,  but  become  flattened,  and 
sometimes  slightly  concave,  toward  the  gingival  line. 

31.  The  roots  of  the  lower  incisors  are  slender  and  much 
flattened  in  their  mesio-distal  diameter,  and  not  unfrequently 
slightly  grooved  on  the  mesial  and  distal  sides.  The  labial 
surface  of  the  crown  and  root,  in  its  length,  forms  nearly  the 
arc  of  a  circle  (Fig.  1-7),  though  the  curve  of  the  surface  of 
the  crown  is  usually  a  little  greater  than  the  root  (Fig.  16). 
The  lingual  surface  is  almost  straight,  but  in  the  apical 
third  it  is  convex,  sloping  away  to  form  the  apex.  The 
roots  of  these  teeth  are  generally  straight,  but  occasionally 
the  apex  is  curved  to  the  distal  side. 


32  THE    CUSPIDS — THE   UPPER   CUSPID. 

THE   CUSPIDS. 

32.  We  have  four  cuspids,  one  on  each  side  in  the 
upper  and  the  lower  jaw.  Thej  are  sometimes  called  canine, 
or  eye,  teeth.  They  are  situated  at  the  angles  of  the  mouth 
between  the  lateral  incisors  and  the  first  bicuspids.  They 
are  the  third  tooth  from  the  median  line,  and  are  large, 
strong  teeth  of  simple  form,  firmly  implanted  in  the  alveolar 
process  by  a  long,  strong  root,  the  longest  in  the  human 
mouth  {q.  v.  tables  of  measurements).  The  name  cuspid  is 
given  to  this  tooth  because  its  crown  is  surmounted  by  a 
single  strong  cusp. 

THE   UPPER   CUSPID. 

33.  The  labial  surface  of  the  crown  of  the  upper  cuspid 
(Fig.  18)  is  a  little  narrower  in  the  mesio-distal  direction 
than  in  the  central  incisor,  with  nearly  equal  length  from 
the  point  of  the  cusp  to  the  gingival  line.  Instead  of  a 
straight,  or  only  slightly  curved-cutting  edge,  as  in  the  in- 
cisors, the  central  portion  of  the  crown  is  extended  into  a 
well-formed  point  (a),  with  a  cutting  edge  sloping  away  to 
the  mesial  and  distal  angles  (^,  h).  Of  these  cutting  edges, 
the  distal  is  a  little  the  longer,  and,  from  the  angle  to  the 
gingival  line,  the  distal  surface  is  a  little  shorter,  than  the 
mesial.  In  unworn  teeth,  the  angle  formed  by  the  union  of 
the  cutting  edges  from  the  cusp  is  usually  about  ninety 
degrees,  or  a  square.  The  point  is  a  little  rounded,  but  the 
cusp  is  soon  much  rounded  or  flattened  by  wear.  Both  the 
mesial  and  distal  margins  of  the  labial  surface  of  the  crown, 
from  the  angles  to  the  gingival  line,  slope  toward  the  central 
axis  of  the  tooth, — the  distal  the  most,  narrowing  the  crown 
of  the  neck  nearly  one-third  from  the  width  of  its  widest 
point.  The  curvature  of  the  gingival  line  on  this  surface, 
marking  the  termination  of  the  crown,  is  about  a  quarter 
circle.  The  surface  is  convex  in  all  directions,  and  is  much 
more   rounded  in  the  mesio-distal   direction,  than  in  the 


Fig.  18. 


Fig.  19. 


Fig.  20. 


Fig.  21. 


Fig.  22. 


Fig.  24. 


Fig  23 

Fig.  18  *  (Par.  33).— Right  Uppee  Cuspid,  Labial  Surface.  a.  Point  of  cusp ; 
d,  labial  ridge ;  e,  labial  grooves  ;  /,  gingival  line  ;  g,  mesial  angle ;  h,  distal  angle ;  i,  body 
of  root ;  k,  apex  of  root. 

Fig.  19  *  (Par.  34).— Right  Upper  Cuspid,  Lingual  Surface.  The  more  common 
form,  a,  Point  of  cusp ;  e,  e,  lingual  grooves ;  d,  gingival  ridge  ;  /,  gingival  line  ;  g,  me- 
sial angle  ;  h,  distal  angle  ;  i,  body  of  root ;  k,  apes  of  root. 

Fig.  20  *  (Par.  34).— Right  Upper  Cuspid,  Lingual  Surface  of  irregular  foi-m. 
a,  Point  of  cusp  ;■.  d,  linguo-gingival  ridge ;  e,  e,  lingual  grooves ;  /,  gingival  line ;  g,  me- 
sial angle ;  h,  distal  angle  ;  m,  prominent  lingual  ridge ;  n,  two  small  tubercles  on  linguo- 
gingival  ridge. 

Fig.  21  *  (Par.  35).— Right  Upper  Cuspid,  Mesial  Surface,  a,  Point  of  cusp ;  b, 
mesial  marginal  ridge  ;  e,  point  of  slight  concavity  of  mesial  surface  ;  d,  linguo-gingival 
ridge  ;  e,  labial  groove  ;  /,  /,  gingival  line ;  g,  mesial  angle  ;  i,  body  of  root ;  k,  apex  of 
root. 

Fig.  22*  (Par.  37).— Left  Upper  Cuspid,  with  a  very  long  and  croolied  root. 

Fig.  23*  (Par.  37).— Right  Upper  Cuspid,  with  a  peculiarly  crooked  root. 

Fig.  24*  (Par.  87).— Left  Upper  Cuspid,  with  a  very  small  and  short  root. 


*  Illustration,  IJ^  diameters. 
c 


THE    UPPER    CUSPID.  35 


incisors.  In  the  direction  of  its  length,  the  convexity  is  about 
the  same  as  in  the  incisors.  The  greater  convexity  mesio- 
distally  is  caused  by  a  strong  labial  ridge  {d)  running  from 
the  point  of  the  cusp  to  the  gingival  line.  This  ridge  occu- 
pies so  much  of  the  surface  of  the  tooth  that  its  margins  are 
imperfectly  defined.  It  belongs  to  the  middle  lobe,  developed 
from  the  middle  plate,  which,  in  the  incisors,  is  the  smallest 
of  the  three,  but  in  this  tooth  is  much  the  largest.  There  are 
two  labial  furrows  (e),  or  a  flattening  of  the  convexity  between 
the  central  line  of  the  ridge  and  each  angle,  marking  the 
junction  of  the  lobes.  These  furrows  are  usually  lost  by 
becoming  shallower  before  reachino;  the  center  of  the  lenscth 
of  the  crown.  In  well-formed  teeth,  this  surface  presents  a 
uniform  enamel,  free  from  pits  or  sulci. 

34.  The  lingual  surface  (Fig.  19)  presents  the  same 
general  marginal  configuration  as  the  buccal,  though  it  is 
somewhat  narrower  toward  the  gingival  line.  This  is  caused 
by  the  arc  of  convexity  being  a  smaller  circle,  and  by  the 
flattening  of  the  proximate  surfaces  on  lines  which  converge 
rapidly  to  the  lingual.  This  surface  is  usually  almost 
straight  from  the  cusp  to  the  gingival  ridge,  or  cingulum, 
but  is  sometimes  slightly  concave.  The  gingival  ridge  is 
sharply  convex  and  longer  from  the  gingival  line  to  the 
point  of  convexity  than  in  the  incisors.  (Fig.  21,  d).  Mesio- 
distally  this  surface  is  slightly  convex  in  its  central  part  on 
account  of  the  lingual  ridge  which  runs  from  the  point  of 
the  cusp  nearly,  or  quite,  to  the  cingulum.  On  each  side  of 
this,  and  between  it  and  the  marginal  ridges,  there  is  a  slight 
but  well  defined  concavity  and  furrow,  marking  the  conflu- 
ence of  the  lobes.  The  marginal  ridges  arise  from  the  mesial 
and  distal  angles  and  unite  with  the  gingival  ridge  or  cingu- 
lum. These  ridges  are  usually  large  near  the  angles,  and 
much  less  pronounced  toward  the  gingival  ridge.  The  latter 
is  prominent,  and  is  often  raised  into  a  tubercle,  or  slight 
cusp.      Occasionally  this  part  of  the  enamel  is  thrown  into 


36  THE   LOWER   CUSPIDS. 


irregular  folds,  with  grooves  between,  which  are  sometimes 
fissured.  More  rarely  the  small  cusp  may  be  divided  by  a 
groove  (Fig.  20,  n).  The  linguo-gingival  groove  is  often 
pronounced  in  unworn  teeth. 

35.  The  mesial  surface,  near  the  angle  (Fig.  21),  is 
convex  in  all  directions,  but  becomes  flattened,  and  occasion- 
ally sightly  concave,  near  the  gingival  line  (c). 

36.  The  distal  surface  is  similar  to  the  mesial,  but  ia 
more  convex,  usually  being  well  rounded  in  the  labio-lingual 
direction  to  the  gingival  line.  But  in  the  direction  of  the 
long  axis  of  the  tooth  this  surface,  on  account  of  the  projec- 
tion of  the  distal  angle,  is  first  convex,  and  further  toward 
the  gingival  line  is  concave,  especially  near,  and  at  the  neck 
of  the  tooth.  The  labio-lingual  curvature  of  the  gingival 
line  is  about  2.5  m.m.,  varying  from  1.0  m.m.  to  3.5  m.m.  on 
the  mesial  surface,  and  a  little  less  on  the  distal. 

37.  The  root  of  the  upper  cuspid  is  the  longest  in  the 
human  mouth,  averaging,  according  to  my  measurements, 
17.5  m.m.,  and  varying  from  11.0  to  21.0  from  the  apex  to 
the  gingival  line  at  the  buccal  surface.  It  is  irregularly 
conical  in  form,  tapering  from  the  neck  to  the  apex.  Its 
labio-lingual  diameter  is  a  little  greater  than  its  mesio-distal, 
which  gives  the  root  a  flattened  appearance,  but  it  is  seldom 
entirely  flat  on  either  the  mesial  or  distal  surface.  In  most 
examples  the  body  of  the  root  is  straight,  and  tapers  to  a 
slender  point,  which  is  often  curved  to  the  labial  and  distal, 
though  the  form  of  this  root  presents  great  variations.  Fre- 
quently, it  is  very  crooked,  perhaps,  because,  when  it  is  taking 
its  place  in  the  arch,  it  is  often  crowded  by  the  teeth  mesial 
and  distal  to  it,  so  that  its  growth  in  a  right  line  is  inter- 
rupted.    (See  Figs.  22,  23  and  24). 

THE   LOWER   CUSPIDS. 

38.  In  their  general  figure,  the  lower  cuspids  so  closely 
resemble  the  upper,  a  description  of  their  differences  will  be 


Fig.  28. 


Fig.  29. 


Fig.  25*  (Par.  38).— Left  Lower  Cuspid,  Labial  Surface,  a,  Point  of  cusp ;  b,  mesial 
surface ;  c,  distal  surface  ;  d,  labial  ridge ;  e,  distal  labial  groove ;  /,  gingival  line ;  g, 
mesial  angle ;  h,  distal  angle  ;  i,  body  of  root ;  k,  apex  of  root. 

Fig.  26  *  (Par.  38).— Left  Lower  Cuspid,  Mesial  Surface,  a,  Point  of  cusp ;  d,  linguo- 
gingival  ridge ;  /,  gingival  line ;  g,  mesial  angle ;  i,  body  of  root,  which  is  distinctly 
flattened ;  k,  apex  of  root. 

Fig.  27  *  (Par.  38).— Left  Lower  Cuspid,  Distal  Surface,  a,  Point  of  cusp ;  c,  labial 
groove  ;  d,  linguo-gingival  ridge ;  e,  concavity  of  the  distal  cutting  edge  where  the 
groove  passes  over  it ;  /,  gingival  line ;  h,  distal  angle ;  i,  body  of  root ;  k,  apes  of  root. 

Fig.  28*  (Par.  39).— Left  Lower  Cuspid,  Lingual  Surface,  a,  Point  of  cusp;  d, 
linguo-gingival  ridge ;  e,  lingual  grooves ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal 
angle  ;  i,  body  of  root ;  k,  apex  of  root ;  I,  distal  marginal  ridge ;  m,  lingual  or  triangular 
ridge  ;  n,  mesial  marginal  ridge. 

Fig.  29*  (Par.  40).— Right  Lower  Cuspid,  Mesial  Surface,  a,  Point  of  cusp;  d, 
linguo-gingival  ridge  ;/,  gingival  line ;  g,  mesial  angle.    The  root  is  short  and  thick. 


*  Illustration,  IJ^  diameters. 


THE    BICUSPIDS.  S9 


sufficient.  It  is  slightly  smaller  than  the  upper  cuspid,  and 
the  crown  is  a  little  longer,  which  makes  it  appear  more 
slender.  The  mesial  surface  is  usually  nearly  straight  the 
entire  length  of  the  root  and  crown  (Figs.  25  and  26) ;  so 
that  the  increased  width  of  the  crown  over  the  root  is  mainly 
on  the  distal.  This  causes  a  marked  prominence  of  the  dis- 
tal angle.  In  many  examples  this  gives  the  tooth  the  ap- 
pearance of  being  bent,  with  a  considerable  concavity  on  the 
distal  side.  In  young,  unworn  teeth,  the  cusp  is  rather  more 
prominent  and  pointed  than  in  the  upper  cuspid,  and  the 
distal  cutting  edge  is  proportionately  longer;  but,  as  the 
point  of  the  cusp  comes  directly  in  occlusion  with  the  upper 
teeth,  it  is  soon  worn  to  a  blunt  point,  or  a  flat  surface^ 
inclining  to  the  labial,  sloping  away  to  the  distal. 

39.  The  lingual  surface  (Fig.  28)  is  very  smooth,  and 
the  ridges  are  less  prominent  than  in  the  upper  cuspid.  A 
tubercle  on  the  gingival  ridge  is  rare.  The  developmental 
lines,  or  grooves,  are  the  same  as  those  of  the  upper  cuspids,, 
but  less  prominent.  Yet,  generally,  they  can  be  seen  in  un- 
worn teeth.    Fissures  are  seldom  seen  in  any  part  of  this  tooth. 

40.  The  root  of  the  lower  cuspid  (Figs.  25  to  29)  is 
shorter  than  the  upper,  and  generally  more  flattened  in  the 
mesio-distal  diameter,  often  presenting  deep  furrows.  la 
rare  instances,  there  is  a  division  of  the  root  near  the  ex- 
tremity. The  root  is  nearly  straight,  and  in  many  examples 
the  lingual  surface  of  the  root  is  nearly  a  straight  line,  while 
the  buccal  surface,  root,  and  crown,  present  a  nearly  regular 
convexity.  The  root  is  not  so  often  abnormally  crooked  as 
that  of  the  upper  cuspid,  though,  like  the  upper,  the  root  is 
much  inclined  to  end  in  a  slender  apex;  which  is  often 
slightly  bent  in  the  labial  direction. 

THE    BICUSPIDS. 

41.  There  are  eight  bicuspids,  or  premolars,  two  on  each 
side  in  the  upper  jaw,  and  two  on  each  side  in  the  lower  jaw- 


40  UPPER  FIRST  BICUSPID. 

Hence  tliey  are  called  the  first  and  second  bicuspids.  They 
are  situated  between  the  cuspids  and  first  molars,  and  are 
the  fourth  and  fifth  teeth  from  the  median  line.  The  bicus- 
pids, though  unlike  the  incisors  and  cuspids  in  the  contour 
of  their  crowns,  have  the  same  number,  and  a  similar  dis- 
tribution of  primary  parts,  or  lobes.  They  are,  indeed, 
formed  on  the  same  general  plan.  The  change  of  form  is 
the  result  of  a  different  relative  development  of  the  parts, 
by  which  the  cingulum,  or  gingival  ridge,  is  elevated  into  a 
powerful  lingual  cusp ;  which,  in  the  upper  bicuspids,  is  almost 
or  quite  as  high  as  the  buccal  cusp,  but  in  the  lower  bicuspids, 
especiallj"  in  the  first,  this  is  less  prominent.  The  central 
lobe  also  forms  a  relatively  larger  part  of  the  buccal  portion 
of  the  crown  than  in  the  incisors  and  cuspids ;  while  the 
mesial  and  distal  lobes  are  relatively  smaller.  By  the  de- 
velopment of  the  lingual  cusp  of  the  upper  bicuspids,  the 
linguo-gingival  groove  of  the  incisors  and  cuspids  {q.  v.  21) 
is  carried  to  the  central  part  of  the  crown,  which  it  traverses 
from  mesial  to  distal  in  a  deep  sulcus  (Fig.  30).  It  is  natu- 
rally divided  by  the  mesial  and  distal  pits,  found  at  its 
junction  with  the  triangular  grooves,  into  three  parts :  me- 
sial (o),  central  (/),  and  distal  [jp).  In  the  lower  bicuspids 
"the  lingual  lobe  is  often  very  small  and  the  course  of  the 
grooves  irregular. 

UPPER   FIRST   BICUSPID. 

42.  The  outline  of  the  occluding  surface  of  the  upper 
first  bicuspid  (Fig.  30),  when  seen  in  a  line  with  the  long 
axis  of  the  tooth,  is  irregularly  quadrilateral,  or  trapezoidal 
in  form.  The  bucco-lingual  diameter  is  about  two-ninths 
greater  than  the  mesio-distal.  The  flattened  proximate 
surfaces  converge  toward  the  lingual,  so  that  the  mesio-distal 
measurement  of  the  buccal  portion  is  a  little  greater  than 
the  lingual.  The  buccal  and  lingual  surfaces  are  convex. 
The  buccal  convexity  forms  an  arc  of  about  a  quarter  circle, 
and  merges  into  the  proximate  surfaces  by  obtuse,  but  well 


Fig.  30. 


Fig.  32. 


Fig.  33. 


Fig.  34. 


Fig.  30*  (Par.  42).— Right  Upper  Fiest  Bicuspid,  Occluding  Subface.  a,  Point  of 
buccal  cusp ;  b,  lingual  cusp ;  c,  buccal  ridge ;  d,  mesial  marginal  ridge  ;  e,  distal  margi- 
nal ridge ;  /,  triangular  ridge  of  the  buccal  cusp ;  g,  distal  angle ;  h,  mesial  angle ;  i, 
triangular  ridge  of  the  lingual  cusp;  I,  central  groove;  o,  mesial  groove;  p,  distal 
groove ;  n,  m,  triangular  grooves ;  r,  s,  buccal  grooves. 

Fig.  31*  (Par.  46).— Right  Upper  First  Bicuspid,  Buccal  Surface,  a,  Buccal  cusp; 
c,  buccal  ridge ;  e,  e,  buccal  grooves ;  /,  gingival  line ;  g,  mesial  angle ;  h,  distal  angle ; 
i,  buccal  root ;  k,  lingual  root. 

Fig.  32  *  (Par.  48).— Right  Upper  First  Bicuspid,  Mesial  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp ;  c,  mesial  angle ;  d,  mesial  surface  and  point  where  there  is  often  a  con- 
cavity ;  /",/,  gingival  line ;  e,  lingual  root ;  g,  buccal  root. 

Fig.  33  *  (Par.  50).— Upper  First  Bicuspid,  Avith  three  roots.    Bucco-mesial  angle. 

Fig.  34*  (Par.  50).— Upper  First  Bicuspid,  with  three  short  roots  and  of  a  peculiar 
form. 

Fig.  35*  (Par.  50).— Upper  First  Bicuspid,  with  a  single,  very  long,  crooked  root. 


*  Illustration,  1}^  diameters. 


UPPER   FIRST  BICUSPID.  43 


defined,  angles  (A,  g).  The  lingual  surface  forms  an  arc  of 
nearly  half  a  circle,  and  merges  into  the  proximate  surfaces 
without  any  angular  prominence. 

43.  The  occluding  surface  has  two  prominent  cusps — 
the  buccal  («),  and  the  lingual  (6) — and  is  transversed  from 
mesial  to  distal  by  a  deep  sulcus.  The  buccal  cusp  is  the 
larger,  and  forms  the  terminal  point  of  the  buccal  surface. 
From  the  point  of  this  cusp,  four  ridges  lead  away  at  right 
angles.  Two  of  these  form  cutting  edges,  which  slope  away 
mesially  and  distally  to  the  mesial  (A)  and  distal  angles  (^), 
where  they  join  the  marginal  ridges.  The  central  buccal 
ridge  (c)  leads  away  centrally  on  the  buccal  surface  toward 
the  gingival  line,  forming  the  convexity  of  this  surface. 
The  triangular  ridge  (/)  slopes  down  to  the  central  part  of 
the  crown  and  joins  a  similar  ridge  from  the  lingual  cusp 
(i)  to  form  the  transverse  ride,  or  ends  in  a  central  sulcate 
groove  {I).  The  lingual  cusp  (6)  is  in  the  form  of  a  crescent ; 
its  convexity  forms  the  occluding  margin  of  the  lingual 
surface.  Instead  of  a  well  defined  point  it  usually  presents 
a  blunt  edge,  which  runs  around  its  elevated  central  portion, 
and  joins  with  the  marginal  ridges  at  both  angles.  The 
lingual  triangular  ridge  {i)  leads  down  from  the  central 
point  of  the  cusp  to  the  central  groove,  to  join  its  fellow 
from  the  buccal  cusp  in  the  formation  of  the  transverse 
ridge,  or  is  divided  from  it  by  a  deep  central  sulcate  groove. 
The  ridge  is  seldom  prominent.  Yery  frequently  the  central 
incline  of  the  lingual  cusp  is  a  plain  surface. 

44.  The  marginal  ridges,  mesial  {d)  and  the  distal  (e), 
are  strong  ridges  of  enamel  which  rise  in  the  mesial  and 
distal  terminations  of  the  cutting  edges  of  the  buccal  cusp,  and 
form  the  mesial  and  distal  margins  of  the  occluding  surface. 
They  join  with  the  ridge  forming  the  lingual  cusp.  Or  they 
are  usually  divided  from  the  latter  by  the  mesial  and  distal 
grooves ;  though  the  latter  are  often  indistinct,  especially 
in  teeth  that  have  been  somewhat  worn. 


44  UPPER  FIRST   BICUSPID. 

45.  The  occluding  surface  of  the  bicuspid  has  five 
developmental  grooves ;  the  central  (1),  mesial  (o),  distal  (p), 
mesial  triangular  (?n),  and  distal  triangular  (n).  The  central 
groove  is  deeply  sulcate,  and  divides  the  triangular  ridges, 
or  passes  over  their  junction  as  a  shallow  line,  and  sinks  into 
a  triangular  pit  at  either  end.  The  mesial  and  distal  grooves 
are  really  continuations  of  the  central,  which  pass  over  the 
marginal  ridges  as  very  fine  lines,  or  as  more  marked  grooves, 
and  mark  the  boundary  of  the  lingual  lobe.  They  are  rarely 
fissured,  while  the  central  groove  is  frequently  fissured 
throughout  its  course.  The  triangular  grooves,  mesial  (m) 
and  distal  (w),  run  from  the  mesial  and  distal  pits  toward 
the  mesial  and  distal  angles,  dividing  the  marginal  ridges 
from  the  triangular.  They  are  occasionally  sulcate  in  the 
first  part  of  their  course,  and  are  generally  lost  toward  the 
buccal  angles  by  becoming  shallower ;  but  in  young,  unworn 
teeth  they  can  often  be  followed  as  a  fine  line  running  over 
the  cutting  edges  of  the  buccal  cusp  near  the  angles,  and 
leading  into  the  buccal  grooves  (r,  s).  These  are  the  marks 
of  confluence  of  the  mesial  and  distal  lobes  with  the  median 
or  central  lobe.  In  the  central  incline  of  the  lingual  cusp, 
supplemental  grooves  are  often  seen  meeting  the  triangular 
grooves  of  the  buccal  side.  The  triangular  grooves  are 
occasionally  fissured  for  a  short  distance  from  their  junction 
with  the  central. 

46.  The  buccal  surface  of  the  upper  first  bicuspid  (Fig. 
SI)  is  similar  to  the  labial  surface  of  the  cuspid  {q.  v,  33). 
The  cusp  is  usually  nearer  the  center  of  the  crown,  and 
generally  somewhat  to  the  distal ;  therefore,  the  cutting 
edges  which  run  from  the  summit  of  the  cusp  to  either 
angle  may  be  of  about  equal  length.  In  some  examples  the 
distal  edge  is  the  longer ;  but  usually  the  mesial  edge  is  the 
longer.  In  the  gingival  half  of  its  length  this  surface  is 
smoothly  convex  from  mesial  to  distal ;  but  further  toward 
the  occluding  margin,  the  buccal  ridge,  which  terminates  in 


UPPER   FIRST   BICUSPID.  45 

the  cusp,  becomes  more  prominent,  and  a  shallow  buccal 
groove  (e,  e)  appears  at  both  sides  of  the  ridge,  or  between 
it  and  the  angles.  This  surface  is  also  considerably  narrowed 
toward  the  gingival  border,  almost  equally  on  the  mesial 
and  distal,  so  that  the  crown  seems  much  broader  at  the 
occluding  surface. 

47.  The  lingual  surface  is  regularly  convex  from  mesial 
to  distal.  From  the  gingival  margin  to  the  summit  of  the 
lingual  cusp  it  is  often  a  straight  line ;  but  more  generally  it 
is  slightly  convex,  in  manj  examples  almost  as  convex  as  the 
buccal  surface. 

48.  The  mesial  surface  (Fig.  32)  is  much  flattened  from 
buccal  to  lingual,  but  is  generally  slightly  convex  over  its 
whole  extent ;  yet  in  many  examples  there  is  a  slight  con- 
cavity near  the  gingival  line.  In  the  direction  from  the 
gingival  line  to  the  occluding  margin,  this  surface  is  slightly 
convex  through  its  whole  length,  but  not  equally  so  through 
its  buccal  and  lingual  half.  The  lingual  portion  is  progress- 
ively more  rounded  toward  the  occluding  surface ;  while  the 
buccal  portion  is  nearly  straight  to  the  angle.* 

49.  The  form  of  the  distal  surface  agrees  substantially 
with  the  mesial,  but  is  rather  more  convex  in  all  directions 
and  any  concavity  is  rare. 

50.  The  root  of  the  upper  first  bicuspid  is  usually  either 
much  flattened  and  grooved  on  its  mesial  and  distal  sides,  or 
separated  into  two  divisions,  one-third  to  two-thirds  of  its 
length,  making  one  buccal  and  one  lingual  root.  More  than 
half  have  their  roots  thus  divided.  When  separated,  the 
roots  taper  regularly  to  slender  apexes.  When  not  divided, 
the  apex  is  apt  to  be  obtuse.  Occasionally  this  tooth  pre- 
sents three  divisions  of  the  root,  two  buccal  and  one  lingual 

*  The  form  of  the  proximate  surfaces  is  especially  important  in  making 
contour  fillings,  for  any  concavity  increases  the  difficulty  of  forming  good, 
clean  margins  at  the  gingival  border.  The  unequal  convexity  of  the  buccal 
and  lingual  halves  is  important,  and  requires  a  special  adaptation  of  instru- 
ments to  make  a  perfect  contour  and  good  clean  margins. 


46  UPPER    SECOND    BICUSPID. 

(Figs.  33,  34).     In  some  instances  the  root  of  this  tooth  is 
very  crooked  or  otherwise  distorted  (Fig.  35). 

UPPER   SECOND   BICUSPID. 

51.  The  upper  second  bicuspid  so  nearly  resembles  the 
upper  first,  just  described,  that  a  notice  of  its  differences 
will  be  sufficient.  It  is  a  little  smaller,  and  in  every  way 
more  slender.*  The  general  form  of  the  occluding  surface 
(Fig.  36)  is  similar  to  the  first  bicuspid.  It  presents  a  buccal 
and  a  lingual  cusp,  and  similar  sulcus,  ridges,  grooves,  and 
pits.  The  average  height  of  the  cusps  is  considerably  less 
than  in  the  first  bicuspid.  The  marginal  ridges  are  propor- 
tionally broader,  the  mesial  and  distal  pits  closer  to  each 
other,  and  the  central  groove  shorter.  The  triangular  grooves 
join  the  central  groove  nearer  the  mesio-distal  center  of  the 
tooth,  making  the  buccal  triangular  ridge  narrower  and 
more  nearly  pointed.  In  many  examples  the  enamel  of  the 
occluding  surface  is  thrown  into  several  shallow  wrinkles,  or 
supplemental  grooves  and  ridges,  which  radiate  from  the 
central  groove,  which  occurs  but  rarely  in  the  first  bicuspid. 
The  buccal  cusp  is  a  little  nearer  the  mesial  than  the  distal 
angle,  so  that  the  distal  edge  is  slightly  the  longer. 

52.  From  mesial  to  distal,  the  buccal  surface  (Fig.  37) 
is  not  so  broad  at  the  occluding  surface,  and  is  a  little  broader 
at  the  neck,  so  that  it  has  not  so  much  of  the  bell-crown  ap- 
pearance as  the  first  bicuspid.  Otherwise,  this  surface  has 
the  same,  but  less  definitely  defined,  outlines  and  markings. 
The  mesial  and  distal  surfaces  (Figs.  38  and  39)  are  generally 
slightly  more  convex,  and  the  crown  more  smoothly  rounded. 
The  mesial  surface  seldom  shows  a  concavity.  The  lingual 
surface  is  usually  a  little  more  rounded  toward  the  cutting 
edge  or  crest  of  the  cusp.  Generally,  the  distal  side  of  the 
lingual  cusp  is  rounded  to  such  an  extent  as  to  bring  the 
summit  of  the  cusp  to  the  mesial  of  the  central  line  of  the 

*  The  popular  opinion  is  that  the  second  bicuspid  is  the  larger. 


Fig.  36. 


Pig.  40. 


Fig.  41. 


Fig.  36*  (Par.  51).— Eight  Upper  Second  Bicuspid,  Occluding  Surface,  o,  Point  of 
buccal  cusp ;  6,  lingual  cusp ;  e,  buccal  ridge ;  e,  mesial  marginal  ridge ;  d,  distal  margi- 
nal ridge ;  /,  triangular  ridge  of  the  buccal  cusp ;  g,  mesial  angle ;  U,  distal  angle ;  i,  tri- 
angular ridge  of  the  lingual  cusp ;  I,  central  groove ;  m,  n,  triangular  grooves ;  o,  p, 
buccal  grooves. 

Fig.  37*  (Par.  52).— Right  Upper  Second  Bicuspid,  Buccal  Surface,  a.  Point  of 
buccal  cusp ;  c,  buccal  ridge ;  e,  e,  buccal  grooves ;  /,  gingival  line ;  g,  mesial  angle ; 
h,  distal  angle ;  i,  body  of  root ;  k,  apex  of  root. 

Fig.  38  *  (Par.  52).— Right  Upper  Second  Bicuspid,  Mesial  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp ;  /,  gingival  line ;  i,  groove  in  the  mesial  side  of  the  root. 

Fig.  39  *  (Par.  52).— Right  Upper  Second  Bicuspid,  Distal  Surface,  a,  Buccal  cusp ; 
6,  lingual  cusp ;  c,  carous  cavity  near  the  proximate  contact  point ;  /,  gingival  line  ;  i, 
groove  in  distal  side  of  root. 

Fig.  40*  (Par.  53).— Upper  Second  Bicuspid,  with  a  very  crooked  root. 

Fig.  41*  (Par.  53).— Upper  Second  Bicuspid  with  a  very  short  crook  of  the  root. 


'  Illustration,  IJ^  diameters. 


LOWER   FIRST    BICUSPID.  49 


tooth.  The  gingival  line,  in  its  course  round  the  neck  of 
the  tooth,  makes  but  a  slight  labio-lingual  curvature  on  the 
mesial  surface.  Generally  there  is  no  curvature  on  the  dis- 
tal surface. 

53.  The  root  of  the  upper  second  bicuspid  is  a  little 
longer  than  the  first,  while  the  crown  is  slightly  shorter, 
which  makes  the  proportionate  increase  of  length  appear 
considerable.  The  root  is  rarely  divided  in  any  part  of  its 
length,  but  is  much  flattened  from  the  neck  to  the  apex. 
The  mesial  side  is  often  deeply  grooved  in  the  apical  third  of 
its  length  ;  the  distal  side  is  less  frequently  grooved.  The 
root  tapers  very  gradually,  remaining  broad  in  the  bucco- 
lingual  diameter,  and  ends  in  a  blunt  apex.  A  few  have  a 
root  that  tapers  rapidly,  becomes  more  rounded,  and  ends  in 
a  slender  apex.  Crooked  roots  are  more  frequent  in  this 
than  in  the  other  bicuspids.     (Figs.  40  and  41). 

LOWER   FIRST    BICUSPID. 

54.  This  tooth  is  the  smallest  of  the  bicuspids.  The 
occluding  surface  diflfers  much  from  the  upper  first  bicuspid. 
Indeed,  the  lingual  cusp  is  so  nearly  wanting,  it  would 
hardly  be  called  a  bicuspid  except  for  its  association.  The 
buccal  cusp  is  large  and  prominent,  and  so  much  is  the  buccal 
surface  inclined  toward  the  long  axis  of  the  tooth,  that,  when 
seen  in  a  line  with  the  long  axis  of  the  tooth,  its  jDoint  occu- 
pies a  position  about  one-third  distant  from  the  buccal  to- 
ward the  lingual  outline  of  the  crown  (Figs.  42  and  43).  The 
buccal  cusp  presents  the  same  ridges  leading  from  its  summit 
as  described  for  the  upper  first  bicuspid  (43),  but  the  pair 
which  form  the  cutting  edges  usually  form  a  curve  with  its 
convexity  to  the  buccal,  and  merge  into  the  marginal  ridges 
by  more  rounded  angles.  The  buccal  triangular  ridge  is 
narrow  and  prominent  (/),  and  joins  the  elevated  lingual 
ridge,  or  cusp  (6),  forming  a  complete  transverse  ridge.  In 
many  instances,  this  is  deflected  to  the  mesial  or  distal.     In 


50  LOWER   FIRST    BICUSPID. 

young  teeth,  the  central  groove  often  crosses  the  transverse 
ridge  as  a  fine  line,  which  soon  disappears  by  wear.  How- 
ever, in  many  examples  the  transverse  ridge  is  divided  by  a 
deeply  sulcate  groove.  There  is  a  deep  pit  at  the  mesial  and 
the  distal  ends  of  the  central  groove,  or  on  either  side  of  the 
transverse  ridge  (c,  d)  from  which  the  triangular  grooves, 
which  divide  the  marginal  ridges  from  the  triangular,  or 
transverse  ridge,  run  toward  the  distal  and  buccal  angles. 
These  are  often  sulcate  in  the  first  part  of  their  course.  In 
many  young  teeth  these  grooves  may  be  traced  over  the 
euttino;  eds-es  onto  the  buccal  surface,  markino;  the  confluence 
of  the  central  with  the  mesial  and  distal  buccal  lobes. 

55.  The  lingual  lobe  varies  much  in  its  size  and  outline. 
It  is  divided  from  the  three  buccal  lobes  by  the  mesial,  distal, 
and  central  grooves ;  and  often  occupies  but  a  small  portion 
of  the  lingual  margin  of  the  occluding  surface.  The  grooves 
which  mark  its  outlines  are  often  indistinct,  and  often 
obliterated  by  wear.  The  lobe  may  form  a  ridge  of  even 
height,  and  join  the  marginal  ridges,  or  it  may  be  elevated 
into  one  or  more  tubercles.  It  may,  also,  be  raised  into  a 
small  cusp,  located  centrally,  or  to  either  side  of  the  central 
line  of  the  tooth. 

56.  The  marginal  ridges  are  occasionally  quite  small, 
but  in  most  examples  they  are  well  developed,  and  cause  the 
mesial  and  distal  surfaces  to  stand  out  prominently,  giving 
the  tooth  a  strong  bell-crowned  appearance.  The  length  of 
the  marginal  ridges  vary  with  the  size  of  the  lingual  lobe. 

57.  The  buccal  surface  (Fig.  44)  is  convex  in  all  direc- 
tions. The  cusp  is  to  the  distal  of  its  perpendicular  line, 
and  its  figure  similar  to  the  upper  first  bicuspid,  except  that 
its  surface  is  more  convex.  As  the  occlusion  is  directly  on 
the  point  of  the  cusp,  as  with  the  anterior  lower  teeth  gener- 
ally, it  is  soon  so  worn  down  that  its  prominence  is  lost. 

58.  The  mesial  and  distal  surfaces  are  convex  from 
buccal   to   lino-ual.     In   the   direction   from   the  occluding 


Fig.  45. 


Fig.  46. 


Fig.  47. 


Fig.  42*  (Par.  54).— Right  Lowee  First  Bicuspid,  Occluding  Surface,  a,  Point  ot 
■buccal  cusp ;  &,  lingual  cusp  or  ridge  ;  c,  buccal  ridge ;  d,  mesial  marginal  ridge ;  e,  dis- 
tal marginal  ridge ;  /,  triangular  ridge  of  buccal  cusp  or  buccal  triangular  ridge ;  ff, 
m.esial  angle;  h,  distal  angle;  i,  central  groove  crossing  the  transverse  ridge;  I,  mesial  pit ; 
0,  p,  buccal  grooves. 

Fig.  43  *  (Par.  54).— Lower  First  Bicuspid,  Occluding  Surface,  a,  Point  of  buccal 
cusp ;  6,  lingual  cusp  or  ridge ;  c,  triangular  ridge  of  buccal  cusp  deflected  to  one  side ; 
d,  triangular  groove  with  fissure  ;  e,  mesial  marginal  ridge ;  /,  distal  marginal  ridge. 

Fig.  44  *  (Par.  57).— Right  Loaver  First  Bicuspid,  Buccal  Surface,  a,  Buccal  cusp ; 
d,  buccal  ridge ;  e,  e,  buccal  grooves ;  /,  gingival  line  ;  g.  distal  angle  ;  h,  mesial  angle  ; 
i,  body  of  root ;  k,  apes  of  root. 

Fig.  45*  (Par.  58).— Left  Lower  First  Bicuspid,  Mesial  Surface,  o.  Buccal  cusp; 
b,  lingual  cusp  or  ridge ;  c,  distal  marginal  ridge  ;  d,  triangular  ridge  of  buccal  cusp ;  e, 
mesial  marginal  ridge ;  /,  gingival  line. 

Fig.  46  *  (Par.  59).— Left  Lower  First  Bicuspid,  Lingual  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp  or  ridge  ;  c,  distal  marginal  ridge ;  d,  triangular  ridge  of  buccal  cusp ;  e, 
m.esial  marginal  ridge  ;  /,  gingival  line. 

Fig.  47  *  (Par.  59).— Right  Lower  First  Bicuspid,  Lingual  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp  or  ridge  ;  d,  triangular  ridge  of  buccal  cusp  ;  e,  e,  marginal  ridges ;  /, 
gingival  line. 


=  Illustration,  IJ^  diameters. 


LOWER   SECOND   BICUSPID.  53 

margin  to  the  gingival  line,  they  are  generally  concave,  after 
passing  the  convexity  of  the  immediate  occluding  margin. 
This  latter  stands  out  boldly  to  both  mesial  and  distal,  giving 
a  marked  bell-crowned  form.  The  concavity  of  the  mesial 
and  distal  surfaces  is  not  so  well  seen  from  the  buccal  view  as 
from  the  lingual.  The  greater  over-hang  of  the  crown  (over  the 
root),  and  the  greater  concavity,  is  toward  the  lingual  portion. 

59.  The  lingual  surface  (Figs.  46  and  47)  is  smoothly 
rounded  from  mesial  to  distal,  and  slightly  convex  in  the 
direction  of  the  length  of  the  tooth.  It  is  only  about  half 
as  long  as  the  buccal  surface  (in  unworn  teeth),  and  when 
viewed  at  right  angles  with  the  long  axis  of  the  tooth,  all  of 
the  occluding  surface  on  the  lingual  side  of  the  buccal  cusp 
is  seen  except  the  pits  and  sulci. 

60.  The  neck  of  the  tooth  is  much  constricted,  and  has 
a  deep  gingival  line  at  the  junction  of  the  enamel  and  ce- 
mentum.  This  makes  the  proper  adjustment  of  a  band  for 
an  artificial  crown  particularly  diflacult.  The  curvature  of 
the  gingival  line  is  much  less  than  in  the  upper  first  bicus- 
pid, the  average  being  less  than  one  millimeter  {q.  v.  table  of 
measurements). 

61.  The  root  of  this  tooth  is  somewhat  flattened  at  the 
neck,  on  lines  that  converge  rapidly  toward  the  lingual,  and 
often  grooved  on  its  mesial  and  distal  sides,  and  sometimes 
the  root  is  bifurcated.  It  tapers  regularly,  with  a  tendency 
to  a  more  nearly  round  form  at  the  apex,  and  generally  ends 
in  a  slender  point.  The  root  is  generally  straight,  or  the 
lingual  surface  is  straight,  and  the  buccal  surface  convex. 
This  convexity  extends  from  the  apex  of  the  root  to  the 
point  of  the  crown,  which  gives  that  characteristic  appear- 
ance so  peculiar  to  the  anterior  lower  teeth. 

LOWER   SECOND   BICUSPID. 

62.  The  lower  second  bicuspid  is  a  little  longer  than 
the  lower  first,  and  of  much  the  same  figure,  except  that  the 


54  LOWER   SECOND   BICUSPID. 

lingual  cusp  is  proportionately  higher  and  more  nearly,  hut 
never  quite,  on  a  level  with  the  buccal,  but  the  lingual  sur- 
face is  about  equal  to  the  buccal  in  mesio-distal  breadth. 
These  teeth  are  regular  in  general  contour,  but  the  grooves 
of  the  occluding  surface  are  much  diversified.  These  differ- 
ences may  be  classified  under  three  forms :  1st.  The  central 
groove  joins  the  triangular  grooves  in  such  a  way  as  to  form 
a  half  circle  with  the  convexity  to  the  lingual,  with  or  with- 
out a  transverse  ridge  crossing  its  line.  In  these,  when  the 
transverse  ridge  is  high,  only  a  deep  pit  appears  on  either 
side  (Fig.  48).  2d.  The  lingual  cusp  is  divided  by  a  sulcate 
groove,  which  runs  over  centrally,  or  nearly  so,  to  the  lingual 
surface,  making  a  three-cusped  tooth  (Fig.  49).  The  central 
groove  forms  an  angle  at  the  junction  with  the  lingual,  or  is 
crescentic  in  form.  It  joins  with  the  triangular  grooves  in 
such  a  way  that  the  point  of  junction  cannot  be  told  except 
by  finding  the  mesial  and  distal  grooves,  which  are  often 
very  indistinct.  3d.  The  central  groove  is  straight,  and 
generally  sulcate,  with  a  deep  pit  at  both  ends.  In  many 
examples  these  pits  are  crossed  by  the  triangular  grooves 
almost  at  right  angles  with  the  central  (Fig.  50).  By  trac- 
ing the  fine  mesial  and  distal  grooves  carefully  in  young, 
unworn,  teeth,  it  will  be  found  that  the  lingual  lobe  is  much 
larger  than  in  the  lower  first  bicuspid,  and  almost  as  large  as 
in  the  upper  bicuspids.  In  the  three-cusped  forms  the  two 
lingual  lobes  are  usually  a  little  broader  from  mesial  to  dis- 
tal than  the  buccal  portion  of  the  tooth. 

63.  The  buccal  surface  (Fig.  51)  of  the  lower  second 
bicuspid  does  not  differ  from  the  other  bicuspids,  except 
in  being  shorter,  the  cusp  lower,  and  the  lingual  surface 
(Fig.  52)  broader  and  smoothly  convex  ;  in  the  three-cusped 
forms  it  is  often  somewhat  flattened  and  grooved  in  its 
occluding  third,  giving  the  crown  a  squarish  appearance, 
or  even  triangular  when  the  lingual  lobes  are  large. 

64.  The  mesial  and  distal  surfaces  in  these  bicuspids  are 


Fig.  49. 


Fig.  50. 


Fig.  51. 


Fig.  52. 


Fig.  53. 


Fig.  48*  (Par.  62).— Left  Lower  Second  Bicuspid,  Occluding  Surface,  a,  Buccal 
cusp  ;  6,  lingual  cusp  or  ridge  ;  c,  e,  marginal  ridges ;  d,f,  pits ;  g,  h,  triangular  grooves. 

Fig.  49*  (Par.  62).— Right  Lower  Second  Bicuspid,  Occluding  Surface,  with,  three 
cusps,  a,  Buccal  cusp  ;  b,  disto-lingual  cusp ;  c,  mesio-lingual  cusp ;  d,  lingual  groove ; 
e,  e,  mesial  and  distal  grooves. 

Fig.  50  *  (Par.  62).— Right  Lower  Second  Bicuspid,  Occluding  Surface,  with  straight 
central  groove,  a,  Buccal  cusp ;  6,  lingual  cusp ;  c,  e,  marginal  ridges  ;  d,  triangular 
ridge  of  the  buccal  cusp ;/,  central  groove ;  g,  h,  triangular  grooves. 

Fig.  51  *  (Par.  63).— Left  Lower  Second  Bicuspid,  Buccal  Surface,  a,  Buccal  cusp ; 
d,  buccal  ridge ;  e,  e,  buccal  grooves ;/,  gingival  line ;  g,  mesial  angle ;  /(,  distal  angle ;  i, 
body  of  root ;  k,  apex  of  root. 

Fig.  52  *  (Par.  63).— Right  Lower  Second  Bicuspid,  Lingual  Surface,  a,  Buccal  cusp ; 
b,  lingual  cusp ;  c,  distal  marginal  ridge ;  d,  triangular  ridge  of  the  buccal  cusp ;  e,  mesial 
marginal  ridge ;  /,  gingival  line. 

Fig.  53*  (Par.  64).— Left  Lower  Second  Bicuspid,  Mesial  Surface,  a,  Buccal  cusp; 
5,  lingual  cusp ;  d,  triangular  ridge ;  e,  mesial  marginal  ridge ;  f,  gingival  line ;  i,  groove 
in  mesial  side  of  the  root. 


*  Illustration,  IJ^  diameters. 


THE  MOLAR  TEETH — THE  UPPER  MOLARS.        57 

a  little  flattened,  but  remain  convex  from  buccal  to  linsual. 
Ifrom  the  occluding  margin  to  the  gingival  line,  they  are 
nearly  straight,  though  some  are  convex  and  some  in  part 
concave. 

65.  The  root  of  the  lower  second  bicuspid  is  larger 
and  longer  than  in  the  first  bicuspid.  It  is  flattened  on  the 
mesial  and  distal  surfaces  on  nearly  parallel  lines.  In  some 
examples  they  are  concave  or  grooved.  In  rare  instances 
the  root  of  this  tooth  is  grooved  on  the  buccal  and  lingual 
sides,  with  a  tendency  to  a  division  into  a  mesial  and  distal 
prong.  In  the  greater  number  it  tapers  regularly  to  a  slender 
apex,  but  in  many,  the  apex  is  large  and  obtuse.  The  root 
is  generally  straight,  but  occasionally  very  crooked. 

THE  MOLAR  TEETH. 

66.  The  molar  teeth  are  very  different  in  form  and 
plan  of  construction  from  those  previously  described.  They 
are  particularly  designed  for  grinding  or  comminuting  food  ; 
for  this  purpose  have  broad,  occluding  surfaces,  broken  by 
ridges,  grooves,  and  fossse.  The  ridges  are  raised  at  intervals 
into  powerful  cusps,  which  fit  with  more  or  less  accuracy  into 

the  sulci  and  fossae  of  the  opposing  teeth.  There  are  twelve 
molars,  three  on  each  side  of  both  jaws.  They  are  the  sixth, 
seventh  and  eighth  teeth  from  the  median  line,  and  are  com- 
monly named  the  first,  second  and  third  molars,  upper  and 
lower.  The  last  is  also  called  the  wisdom  tooth,  or  Dens 
Sapientia.  The  upper  and  lower  molars  are  much  alike  in 
size  and  general  contour,  but  in  the  detail  of  the  arrange- 
ment of  their  lobes,  cusps,  fossae  and  grooves,  they  are  dif- 
ferent. It  will,  therefore,  be  necessary  to  describe  the  upper 
and  lower  molars  separately. 

THE    UPPER   MOLARS. 

67.  The  three  upper  molars  are  similar,  but  present 
minor  differences  of  detail,  consisting  mostly  in  a  less  pro- 


58  UPPER    FIRST    MOLAR. 


nounced,  or  typical  development  of  certain  parts,  or  lobes, 
of  the  second  and  third  molars.  The  upper  first  molar  being 
the  typical  form,  will  be  described  first,  and  afterward  the 
deviations  from  this  type  that  occur  in  the  second  and  third, 
molars. 

UPPER   FIRST    MOLAR. 

68.  The  occluding  surface  of  the  upper  first  molar  (Fig. 
54),  when  seen  in  a  line  with  the  long  axis  of  the  tooth,  pre- 
sents an  outline  of  irregular  rhombic  form,  with  the  mesio- 
buccal  and  disto-lingual  as  acute  angles.  The  angles  are 
rounded,  with  more  or  less  convexity  of  the  marginal  lines. 
This  surface  presents  two  principal  fossae,  and  four  devel- 
opmental grooves.  These  grooves  divide  the  crown  into 
four  lobes,  or  primary  developmental  parts,  each  of  which  is 
surmounted  by  a  strong  cusp.  These  lobes,  or  cusps,  are  the 
mesio-buccal  (Fig.  54,  a),  disto-buccal  (6),  mesio-lingual  (c), 
and  disto-lingual  {d).  Of  the  grooves  which  outline  these 
parts,  three  rise  from  the  ceutral  pit  of  the  central  fossa : 
The  mesial  (A),  which  runs  to  the  mesial  margin ;  the  buccal 
(^),  which  runs  in  a  deep  sulcus  to  the  buccal  margin,  and 
over  it  onto  the  buccal  surface ;  and  the  distal  (^"),  which 
runs  distally,  and  lingually,  over  the  transverse  ridge  and 
ends  in  the  distal  fossa  {k).  The  remaining  groove — the 
disto-lingual  (^,  k) — begins  a  little  to  the  buccal  of  the  cen- 
tral part  ot  the  distal  margin,  and  runs  diagonally  in  a 
straight  line,  or  in  a  curve  with  the  concavity  toward  the 
disto-lingual  angle,  to  the  lingual  margin,  and  over  it  onto 
the  lingual  surface,  to  become  the  lingual  groove.  Except 
that  part  crossing  the  distal  marginal  ridge,  this  groove  is 
usually  deeply  sulcate. 

69.  In  their  origin,  each  distinct  portion  begins  its 
calcification  as  a  separate  piece,  plate,  or  cusp,  and  moves 
apart  from  the  others  as  growth  proceeds,  till  the  proper  di- 
mensions of  the  occluding  surface  is  attained ;  then  they 
coalesce  on  the  lines  marked  by  these  grooves,  and  thus  com- 


Fiff.  58. 


Fig.  54*  (Par.  68.)— Right  Upper  First  Molar,  Occluding  Surface,  witli  four  cusps. 
a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  xaesio-lingual  cusp ;  d,  disto-lingual  cusp ; 
f,  mesial  marginal  ridge ;  g,  distal  marginal  ridge ;  h,  mesial  groove ;  i,  buccal  groove  ;  j, 
distal  groove  ;  k,  k,  disto-lingual  groove ;  m,  mesio-buccal  triangular  groove ;  n,  disto- 
buccal  triangular  ridge ;  this  unites  with  the  distal  ridge  from  the  lingual  cusp  to  form 
the  oblique  ridge ;  o,  disto-buccal  triangular  groove ;  p,  mesio-buccal  triangular  ridge ;  q, 
central  pit. 

Fig.  55*  (Par.  70).— Right  Upper  First  Molar,  Occluding  Surface,  with  five  cusps. 
a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ; 

e,  fifth  cusp ;  /,  mesial  marginal  ridge ;  g,  distal  marginal  ridge ;  h,  mesial  groove ;  i, 
buccal  groove ;  j,  distal  groove ;  k,  k,  disto-lingual  groove ;  I,  k,  mesio-Ungual  groove. 
The  Ungual  cusps  are  faceted  by  wear ;  m,  mesio-buccal  triangular  groove ;  n,  disto- 
buccal  triangular  ridge. 

•  Fig.  56*  (Par.  78).— Right  Upper  First  Molar,  Buccal  Surface,    a,  Mesio-buccal 
cusp ;  6,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ;  e,  buccal  ridge ; 

f,  gingival  line  ;  g,  mesial  angle ;  h,  distal  angle ;  i,  buccal  groove ;  k,  mesial  root ;  I,  dis- 
tal root ;  m,  lingual  root. 

Fig.  57*  (Par.  79).— Right  Upper  First  Molar,  Lingual  Surface,  a,  Mesio-buccal 
cusp;  &,  disto-buccal  cusp;  c,  mesio-lingual  cusp;  d,  disto-lingual  cusp;  e,  fifth  cusp; 
f,  gingival  line ;  g,  disto-lingual  groove ;  h,  mesio-lingual  groove ;  i,  lingual  groove ; 
k,  mesial  root ;  I,  distal  root ,  m,  lingual  root. 

Fig.  58*  (Par.  80).— Right  Upper  First  Molar,  Mesial  Surface,  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp ;  e,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ;  e,  fifth  cusp ; 
f,  f,  gingival  line ;  h,  mesio-lingual  groove ;  k,  mesial  root ;  I,  distal  root ;  m,  lingual 
root. 


*  Illustration,  1^  diameters. 


UPPER   FIRST   MOLAR.  61 


plete  the  occluding  surface.  When  the  union  has  been  com- 
pleted, nothing  but  fine  lines  remain,  which,  on  any  plain 
parts,  are  often  quickly  obliterated  by  wear.  But  on  parts 
meeting  at  an  angle,  forming  a  sulcus,  as  in  the  buccal  and 
disto-lingual  grooves,  there  is  usually  a  sharp  groove,  and  at 
any  point  where  the  union  has  been  imperfect,  there  is  a  fis- 
sure. This  fissure  is  most  frequent  at  the  ends  of  the  grooves, 
near  the  central  pit,  or  where  they  are  deeply  sulcate,  and  in 
the  central  portion  of  the  disto-lingual  grooves ;  but  they 
may  occur  in  any  part  of  these  lines. 

70.  In  many  examples  of  the  upper  first  molars,  but  in 
no  others,  there  is  a  small  fifth  lobe  or  cusp  (Fig.  55,  e). 
This  is  situated  on  the  lingual  side  of  the  mesio-lingual  lobe, 
from  which  it  is  divided  by  a  fifth  groove,  the  mesio-lin- 
gual (^,  Z:),  which  runs  from  the  lingual  portion  of  the  mesial 
margin  diagonally  to  the  lingual  margin,  and  joins  the  lin- 
gual groove.  This  cusp,  when  it  occurs,  is  always  bilateral, 
i.e.,  on  both  the  right  and  left  upper  first  molars.  It  is 
hereditary,  appearing  regularly  in  the  teeth  of  children  when 
present  in  the  teeth  of  both  parents.  It  occurs  also,  in  a 
modified  form,  when  present  in  but  one  parent.  Therefore, 
the  cusp  will  be  found  in  all  possible  varieties  of  develop- 
ment, from  its  largest  size,  as  represented  in  Fig.  55,  to  the 
merest  line  marking  its  position  on  the  lingual  side  of  the 
mesio-lingual  cusp. 

71.  The  occluding  surface  of  the  upper  first  molar  has 
four  marginal  ridges,  broken  by  the  grooves  described  (68),  so 
as  to  form  four  principal  eminences  or  cusps.  These  are  the 
buccal,  lingual,  mesial,  and  distal-marginal  ridges.  The 
buccal-marginal  ridge  begins  at  the  mesio-buccal  angle,  in 
the  form  of  a  blunt  cutting  edge,  and  rises  in  a  curved  line 
to  the  summit  of  the  mesio-buccal  cusp  (Fig.  54,  a),  from 
which  it  descends  distally  to  the  buccal  groove  (z).  From  the 
summit  of  this  cusp  the  mesio-buccal  triangular  ridge  (^) 
descends  to  the  mesial  side  of  the  central  pit  {q).   This  ridge 


62  UPPER   FIRST   MOLAR. 


is  divided  from  the  mesial-marginal  ridge  by  the  mesio-buccal 
supplemental  groove  (m),  which  is  sometimes  deep,  but  gen- 
erally shallow,  and  occasionally  absent.  From  the  buccal 
groove  the  marginal  ridge  rises  rapidly  to  the  summit  of  the 
disto-buccal  cusp  (b),  then  descends  in  a  curve  to  the  disto- 
buccal  angle,  to  join  the  distal-marginal  ridge  (g).  From  the 
point  of  this  cusp  the  disto-buccal  triangular  ridge  (or  tri- 
angular ridge  of  the  disto-buccal  cusp,  n),  runs  down  to 
the  distal  side  of  the  central  pit,  where  it  joins  a  ridge  from 
the  mesio-lingual  cusp  to  form  the  oblique  ridge,  or  is  divided 
from  this  ridge  by  a  sulcate  distal  groove. 

72.  The  lingual-marginal  ridge  begins  at  the  mesio- 
lingual  angle  as  a  rounded  edge,  and  rises  in  a  curve  to  the 
summit  of  the  mesio-lingual  cusp  (c),  and  descends,  continu- 
ing its  curve,  into  a  ridge,  meeting  the  triangular  ridge  of 
the  disto-buccal  cusp  to  form  the  oblique  ridge.  However, 
in  a  less  pronounced  form,  this  marginal  ridge  descends  from 
the  summit  of  the  mesio-lingual  cusp  to  the  distal,  where 
it  is  deeply  broken  by  the  disto-lingual  groove.  On  the 
distal  side  of  this  groove  it  rises  abruptly  to  the  summit  of 
the  disto-lingual  cusp  (d),  from  which  it  slopes  away  in  a 
curve  to  join  the  distal-marginal  ridge. 

73.  The  mesial-marginal  ridge  (/)  is  a  strong  band  of 
enamel  running  from  the  mesio-buccal  to  the  mesio-lingual 
angle  of  the  tooth.  It  forms  the  mesial  boundarj-  of  the 
occluding  surface,  and  the  angle  of  junction  of  the  mesial 
and  occluding  surfaces,  or  the  mesio-occluding  angle.  It  is 
low  in  the  center  of  its  length,  and  rises  toward  both  angles. 
It  is  crossed  near  its  center  by  the  mesial  groove,  usually  as 
a  fine  line,  which  is  often  obliterated  by  wear  early  in  life. 
Occasionally  one  or  more  small  tubercles  appear  in  the  cen- 
tral portion  of  this  ridge,  inclosed  in  what  seems  to  be  a 
division  of  the  mesial  groove. 

74.  The  distal-marginal  ridge  (g)  is  a  band  of  enamel 
forming  the  distal  boundary  of  the  occluding  surface,  from 


UPPER   FIRST   MOLAR.  63 


angle  to  angle,  and  forms  the  angle  of  junction  between  the 
occluding  and  the  distal  surfaces,  or  the  disto-occluding 
angle.  It  is  low  in  the  centre  of  its  course,  and  is  crossed 
■by  the  distal  end  of  the  disto-lingual  groove  as  a  fine  line, 
usually  a  little  to  the  buccal  of  the  central  point. 

75.  The  central  fossa  is  irregularly  circular,  and  is 
formed  by  the  central  inclines  of  the  mesial  marginal  ridge, 
Tuesio-buccal  cusp,  disto-buccal  cusp,  mesio-lingual  cusp,  and 
oblique  ridge.  It  is  made  irregular,  and  sometimes  angular, 
by  the  depth  of  the  several  sulcate  grooves,  or  by  the  prom- 
inence of  the  triangular  ridges,  especially  that  from  the 
mesio-buccal  cusp.  The  central  incline  of  the  mesio-lingual 
cusp  is  generally  a  plain  surface,  but  is  sometimes  slightly 
concave,  and  in  about  a  fourth  of  its  examples  there  is  a  low, 
triangular  ridge  running  from  its  apex  directly  to  the  cen- 
tral pit.  The  oblique  ridge  is  occasionally  cut  through  by  a 
deep  and  wide  distal  sulcus,  thus  connecting  the  central  with 
the  distal  fossa.  In  a  few  examples  two  supplemental  grooves 
or  wrinkles  arise  from  the  mesial  groove  at  about  the  center 
of  its  length,  and  run,  one  toward  the  mesio-buccal,  and  the 
other  toward  the  mesio-lingual  angle  of  the  tooth.  These 
are  often  of  such  depth  and  width  as  to  form  a  small  sup- 
plemental mesial  fossa.  Of  these  grooves,  the  mesio-lingual 
is  generally  absent,  and  the  mesio-buccal  (m)  is  generally 
present,  though  often  very  shallow. 

76.  The  distal  fossa  is  formed  by  the  distal  incline  of 
the  disto-buccal  and  mesio-lingual  cusps  and  oblique  ridge, 
which  meet  the  central  incline  of  the  disto-lingual  cusp  and 
distal-marginal  ridge.  It  is  traversed  by  the  disto-lingual 
groove,  which  is  generally  sulcate,  and  deepens  into  a  pit 
at  the  point  where  it  receives  the  distal  groove.  From  the 
buccal  portion  a  supplemental  groove,  the  disto-buccal,  runs 
M^ell  up  toward  the  summit  of  the  disto-buccal  cusp,  divid- 
ing its  triangular  ridge  from  the  distal-marginal  ridge. 

77.  In   some   molars   many   supplemental  grooves   or 


64  UPPER   FIRST   MOLAR, 


wrinkles  radiate  from  the  centers  of  these  fossse  on  the  in- 
clines of  the  ridges  and  cusps,  and  in  some  poorly  developed 
teeth  these  are  deeply  fissured.  The  growth  of  enamel 
seems  to  have  reached  out  toward  the  line  of  junction  in  the 
form  of  spiculse,  and  to  have  failed  to  fill  out  the  space. 

78.  The  buccal  surface  of  the  upper  first  molar  (Fig. 
56)  is  irregularly  convex.  Its  length  is  about  equal  to  the 
mesio-distal  breadth  at  the  gingival  line,  while  the  width  at 
the  widest  point,  near  the  occluding  margin,  is  about  three- 
tenths  greater.  Therefore,  the  mesial  and  distal  margins 
converge  toward  the  neck.  The  mesial  margin  is  almost 
straight,  after  the  rounding  of  its  angle,  but  the  distal  is 
convex.  The  occluding  margin  is  surmounted  by  the  buccal 
cusps  (a,  6),  between  which  there  is  a  deep  notch,  through 
which  the  buccal  groove  passes  from  the  occluding  to  the 
buccal  surface.  This  groove  passes  centrally  toward  the 
gingival  line  about  half  the  length  of  this  surface,  dividing 
the  occluding  portion  into  a  mesial  and  a  distal  buccal  ridge. 
In  some  examples  the  groove  continues  across  the  gingival 
line  to  the  bifurcation  of  the  roots.  There  is  a  bucco-gingi- 
val  ridge  of  enamel  (e)  near  the  gingival  line  which  the 
buccal  groove  generally  does  not  cross.  The  mesio-buccal 
convexity  is  greatest  on  this  ridge,  and  diminishes  toward 
the  occluding  margin.  The  summit  of  this  convexity  is  on 
the  mesial  half,  in  a  line  with  the  mesial  root,  and  the  sur- 
face falls  away  rapidly  toward  the  distal. 

79.  The  lingual  surface  (Fig.  57)  is  divided  in  a  line 
with  the  long  axis  of  the  tooth  into  a  mesial  and  distal  lobe 
by  the  lingual  groove  (z).  Both  lobes  are  smoothly  convex 
from  mesial  to  distal,  and  in  a  less  degree  from  the  gingival 
line  (/)  to  the  occluding  margin.  The  gingival  line  is  nearly 
horizontal,  and  so  sunken  as  to  give  the  appearance  of  a  gin- 
gival enamel  ridge.  The  occluding  margin  is  surmounted 
by  the  mesio-  and  disto-lingual  cusps  (c,  d)^  of  which  the 
mesial  is  usually  the  larger.     In  the  five-cusped  molar  the 


Fia:.  59. 


Fig.  60. 


Fig.  61. 


mp:0^^yJ^'M^^-^''^^^^'-: 


Fig.  62. 


Fig.  59*  (Par.  81).— Right  Uppee,  First  Molar,  Distal  Surface,  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp ;  d,  disto-lingual  cusp ;  /,  /,  gingival  line ;  k,  mesial  root ; 
I,  distal  root ;  m,  lingual  root ;  o,  concavity  of  tlie  distal  surface. 

Fig.  60*  (Par.  82).— Left  Upper  First  Molar,  Buccal  Surface.  A  bell-crowned 
tooth. 

Fig.  61  *  (Par.  8b).— Upper  First  Molar  showing  the  mesial  and  distal  roots  united 
at  their  apexes. 

Fig.  62*  (Par.  86).— The  Right  Upper  Molars  showing  the  progressive  diminution 
of  the  disto-lingual  cusp  from  the  first  to  the  third  molar. 


*  Illustration,  1%  diameters. 


UPPER    FIRST    MOLAR.  67 

fifth  cusp  (e)  is  seen  on  the  mesio-lingual  lobe.  The  mesial 
and  distal  margins  are  convex,  converging  rapidly  toward 
the  lingual  root.  In  the  few  examples  in  which  the  lingual 
groove  is  not  apparent,  the  lingual  surface  is  smoothly  con- 
vex from  mesial  to  distal. 

80.  The  mesial  surface  (Fig.  58)  is  nearly  flat  in  all 
directions,  and  its  margins  are  rounded  to  the  buccal  and 
lingual  surfaces.  Toward  the  mesio-buccal  angle,  the  flat 
surface  is  continued  well  up  to  the  occluding  surface,  which 
it  meets  in  a  fairly  sharp  angle ;  but  as  it  approaches  the 
lingual  portion  it  is  progressively  rounded  toward  the  oc- 
cluding surface.  In  many  molars,  near  the  gingival  line, 
half  way  from  mesial  to  distal,  this  surface  is  a  little  concave. 

81.  The  distal  surface  (Fig.  59),  in  its  lingual  half,  is 
convex  in  all  directions,  but  in  its  buccal  half  there  is  often 
a  concavity  formed  by  a  considerable  distal  protrusion  of  the 
disto-lingual  lobe.  This  is  a  shallow,  but  marked,  depression 
(o),  running  from  the  bifurcation  of  the  distal  and  the  lingual 
roots  toward  the  disto-buccal  cusp.  It  crosses  the  gingival 
line  at  a  point  about  one-third  distant  from  the  buccal  to- 
ward the  distal  margin.  In  many  examples  this  depression 
is  more  central,  and  receives  the  distal  termination  of  the 
disto-lingual  groove,  which  may  often  be  traced  as  a  flne  line 
nearly  or  quite  to  the  gingival  border  of  the  enamel.  This 
complication  of  the  surface  makes  the  finishing  of  fillings, 
and  the  fitting  of  bands  for  crowns,  specially  diflicult.  This 
depression  falls  short  of  forming  a  concavity  in  about  one- 
fourth  of  the  first  molars. 

82.  The  root  of  the  upper  first  molar  (Figs.  56  to  61) 
is  divided  into  three  prongs* — the  mesial,  or  mesio-buccal 

*  The  divisions  of  the  root  of  a  tooth  are  usually  called  "  the  roots,"  and 
the  upper  molars  are  said  to  have  three  roots.  The  neck  of  the  tooth  is, 
however,  common  to  all,  and,  more  strictly,  there  is  one  root  divided  into 
several  prongs,  or  fangs.  Some  authors  follow  this  form  of  expression.  For 
instance,  Prof.  Judd  says:  "The  root  of  a  molar  is  divided  into  three  fangs." 
I  see  no  good  reason,  however,  for  not  calling  them  roots,  the  term  generally 
in  use  by  the  dental  profession. 


68  UPPER    SECOND    MOLAR. 

{k),  the  distal  or  disto-buccal  {I),  and  the  lingual  (m).  These 
are  usually  quite  widely  separated,  giving  the  tooth  a  firm 
seat  in  its  alveolus.  The  lingual  root  is  the  largest ;  it 
diverges  boldly  to  the  lingual,  and  is  straight,  or  slightly 
curved  with  the  convexity  to  the  lingual.  It  is  conical,  and 
tapers  regularly  to  an  obtuse  rounded  apex.  In  most  molars 
it  has  a  groove,  a  continuation  of  the  lingual,  on  its  lingual 
side,  running  nearly,  or  quite,  its  whole  length.  In  rare 
examples  this  root  bifurcates. 

83.  The  mesial  root  (k)  is  larger  than  the  distal ;  broad 
from  labial  to  lingual,  and  thui  from  mesial  to  distal,  with 
the  lingual  portion  the  thinner,  and  grooved  on  its  flattened 
sides.  It  diverges  first  to  the  mesial  and  buccal,  and  then 
curves  to  the  distal.  It  tapers  mostly  at  the  expense  of  the 
lingual  thin  edge,  and  ends  in  a  flattened  or  rounded  apex. 

84.  The  distal  root  {I)  is  the  smallest  of  the  three.  It 
diverges  to  the  distal  and  buccal,  and  is  straight,  or  slightly 
curved,  sometimes  to  the  distal,  sometimes  to  the  mesial,  so 
that  its  apex  approaches  the  mesial  root.  It  is  flattened  on 
its  mesial  and  distal  sides,  but  less  than  the  mesial  root,  and 
tapers  to  a  more  rounded  form,  ending  in  a  slender  point. 

86.  The  roots  of  the  first  molar  are,  perhaps,  more 
regular  in  form  than  those  of  any  other  of  the  molar  teeth; 
but  even  in  these,  considerable  deviation  from  the  forms  de- 
scribed will  occasionally  be  observed  (Figs.  60  and  61). 

UPPER   SECOND   MOLAR. 

86.  The  most  constant  difiference  between  the  occluding 
surfaces  of  the  upper  first  and  second  molars  is  that  the 
latter  tooth  is  smaller,  and  has  an  almost  constant  tendency 
to  a  relatively  smaller  size  of  the  disto-lingual  lobe.  This 
tendency  is  well  seen  in  Fig.  62,  in  which  the  upper  molars 
of  a  very  well  formed  denture  are  drawn  from  the  cast. 
This  shows  the  disto-lingual  lobe  progressively  diminished, 
so  that  in  the  third  molar  it  is  very  small.     When  a  large 


Fig.  65. 


Fig.  66. 


Fig.  67. 


Fig  68. 


Fig.  63*  (Par.  86).— Right  Uppee  Second  Molar,  Occluding  Surface,  witli  three  of 
the  cusps  faceted  by  wear.  Tooth  large  and  especially  well  developed,  a,  Mesio-huccal 
cusp ;  6,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ;  /,  mesial  mar- 
ginal ridge ;  g,  distal  marginal  ridge ;  h,  mesial  groove ;  t,  buccal  groove ;  j,  distal  groove ; 
k,  disto-Ungual  groove ;  I,  distal  fossa ;  m,  mesio-buccal  triangular  groove ;  n.  central  pit ; 
0,  mesio-buccal  triangular  ridge ;  p,  disto-buccal  triangular  ridge ;  r,  mesio-lingual  tri- 
angular ridge, 

Fig.  64*  (Par.  86).— Right  Upper  Second  Molae,  Occluding  Surface.  Tooth  of 
medium  size  and  imperfect  form,  a,  Mesio-buccal  cusp ;  h,  disto-buccal-cusp ;  c,  mesio-  • 
lingual  cusp ;  d,  disto-lingual  cusp ;  /,  mesial  marginal  ridge ;  g,  distal  marginal  ridge ; 
h,  mesial  groove ;  i,  buccal  groove ;  I,  distal  fossa.  The  disto-lingual  groove  is  imperfect ; 
m,  mesio-buccal  triangular  groove ;  o,  mesio-buccal  triangular  ridge ;  p,  disto-buccal  tri- 
angular ridge,  which  unites  with  the  ridge  from  the  mesio-lingual  cusp  to  form  the 
oblique  ridge. 

Fig.  65*  (Par.  87)— Right  Upper  Second  Molar  showing  a  form  of  deformity  peculiar 
to  this  tooth  that  is  not  very  common. 

Fig.  66*  (Par.  89).— Right  Upper  Second  Molar  with  the  roots  inclined  to  the 
distal. 

Fig.  67*  (Par.  90).— Right  Upper  Second  Molar,  Distal  Surface,  with  the  three 
roots  compressed  into  one. 

Fig.  68  *  (Par.  90).— Right  Upper  Second  Molar,  showing  the  distal  and  lingual 
roots  united. 


*  Illustration,  1}^  diameters. 


UPPER   SECOND   MOLAE.  71 


number  of  second  molars  are  examined,  it  is  fomid  that  the 
central  fossa  is  not  so  regularly  formed  as  in  the  first,  being 
often  small,  even  in  large,  well-developed  teeth  (Fig.  63), 
and  the  cusps  comparatively  low,  with  a  relatively  greater 
inclination  of  the  lingual  surface  toward  the  summit  of  the 
mesio-lingual  cusp.  In  many  examples  the  distal  fossa  is 
reduced  to  a  mere  pit  (Fig.  64),  and  the  lingual  marginal 
ridge  is  continued  from  the  summit  of  the  mesio-lingual 
cusp  distally  to  the  disto-lingual  angle,  where  it  joins  the 
distal  marginal  ridge,  as  in  Fig.  64,  making  practically  a 
three-cusped  tooth.  In  many  of  these,  after  the  tooth  is  a 
little  worn,  the  disto-lingual  groove  cannot  be  traced  across 
the  lingual  marginal  ridge,  nor  on  the  lingual  surface ;  but  a 
fine  line  is  generally  seen  crossing  the  distal  marginal  ridge. 

87.  The  upper  second  molar  is  liable  to  a  peculiar 
deformity,  which  I  have  not  seen  in  any  other  tooth.  The 
crown  is  greatly  flattened  from  mesial  to  distal,  occasionally 
to  such  an  extent  as  to  present  none  of  its  usual  lines.  In 
the  extreme  cases  (Fig.  65)  there  is  one  central,  long-shaped 
sulcus  running  from  buccal  to  lingual ,  formed  by  the  central 
inclines  of  a  ridge  encircling  the  occluding  surface.  This 
ridge  may  be  broken  at  intervals  by  shallow  grooves  crossing 
it.  Usually,  much  of  the  central  inclination  of  this  ridge 
is  wrinkled,  and  often  there  are  many  small  fissures.  The 
mesial  surface  is  commonly  deeply  concave,  and  the  distal 
convex. 

88.  In  well-developed  second  molars,  the  form  of  the 
buccal,  lingual,  mesial,  and  distal  surfaces  are  much  the 
same  as  in  the  first  molar,  though  rather  more  convex, 
and  concavities  in  the  mesial  and  distal  surfaces  are  not 
so  frequent.  Howeyer,  in  teeth  with  large  distal  cusps, 
the  concavity  of  the  distal  surface  is  about  the  same  as  in 
the  first  molar  (81).  The  lingual  groove  is  generally  not 
sulcate,  though  it  is  usually  seen  as  a  fine  line  in  unworn 
teeth.     It  is  often  near  the  disto-lingual  angle,  and,  when. 


72  UPPER    THIRD    MOLAR. 


sulcate,  it  generally  disappears  by  becoming  shallower  about 
half-way  toward  the  gingival  line  ;  rarely,  it  runs  across  the 
gingival  line,  and  in  that  case  the  lingual  root  is  grooved,  as 
in  the  first  molars. 

89.  The  neck  of  the  tooth  is  less  regular  in  its  outline 
than  in  the  first  molar.  In  the  average,  it  is  more  flattened 
from  miesial  to  distal,  and  on  lines  that  converge  more  to  the 
lingual.  On  the  buccal  surface,  the  mesio-buccal  ridge  is 
relatively  more  prominent,  and  at  the  neck  the  surface  slopes 
away  more  toward  the  distal,  so  that,  in  many  examples,  the 
distal  root  seems  compressed  between  the  mesial  and  lingual 
roots. 

90.  The  roots  of  this  tooth  are  the  same  in  number  and 
general  form  as  in  the  first  molar;  but  they  spread  less,  and 
are  curved  more  to  the  distal  (Fig.  66).  There  is  also  much 
more  variety  of  the  comparative  size  of  the  root  and  crown 
than  in  the  first  molar.  In  many  the  root  is  single,  with  the 
outlines  of  the  division  marked  by  grooves  of  variable  depth 
(Fig.  67);  or  two  of  the  roots  may  be  connected,  while  the 
third  is  free.     Sometimes  this  union  is  the  lingual  with  the 

"distal  (Fig.  68) ;  but  oftener  it  is  the  lingual  with  the  mesial 
root. 

UPPER   THIRD   MOLAR. 

91.  The  upper  third  molar  deviates  from  the  typical 
form  of  the  first  more  than  does  the  second.  Yet,  in  dent- 
ures of  the  best  form,  it  presents  the  same  developmental 
lines,  fosspe,  and  cusps  (Fig.  69).  The  disto-lingual  lobe  is 
very  much  smaller,  and  in  many  examples  is  entirely  want- 
ing. Of  the  examples  in  my  possession,  about  twenty-one 
per  cent,  show  a  diminutive  disto-lingual  cusp ;  thirty-two 
per  cent,  show  a  pit  in  the  position  of  the  distal  fossa,  and 
some  portion  of  the  disto-lingual  groove,  but  no  depressed 
groove  over  the  lingual-marginal  ridge ;  it  is  similar  to  that 
shown  in  Fig.  64.  The  remainder,  or  about  forty-seven  per 
cent.,  have  no  disto-lingual  lobe.  Of  the  latter,  three-fourths 


^.\r^.<K   ^t^ 


Fig.  72. 


FxG.  69  ^■-  (Par.  91).— Right  Upper  Third  Molar,  Occluding  Surface,  of  typical  form. 
■a,  Mesio-buccal  cusp ;  &,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-Ungual  cusp ; 
e,  mesial  marginal  ridge ;  /,  distal  marginal  ridge ;  g,  mesio-buccal  triangular  ridge ;  li, 
disto-buccal  triangular  ridge ;  i,  mesial  groove ;  l\  buccal  groove ;  I,  distal  groove ;  m 
disto-lingual  groove ;  n,  central  pit ;  o,  mesio-buccal  triangular  groove. 

Fig.  70*  (Par.  91).— Right  Upper  Third  Molar,  Occluding  Surface,  three  cusped.  a, 
Mesio-buccal  cusp ;  h,  disto-buccal  cusp ;  c,  lingual  cusp ;  e,  mesial  marginal  ridge ;  h, 
distal  marginal  ridge ;  i,  mesial  groove ;  k,  buccal  groove ;  I,  distal  groove ;  o,  mesio- 
buccal  triangular  groove. 

Fig.  71*  (Par.  91).— Right  Upper  Third  Molar,  Occluding  Surface.  Young,  unworn 
tooth  of  imperfect  form,  a,  Mesio-buccal  cusp ;  h,  disto-buccal  cusp ;  c,  lingual  cusp ;  e, 
mesial  marginal  ridge;  /,  distal  marginal  ridge;  (/,  mesial  groove;  /(,  buccal  groove; 
i,  distal  groove.    Several  supplemental  grooves  are  seen  radiating  from  the  central  pit. 

Fig.  72*  (Par.  94).— Right  Upper  Third  Molar,  Buccal  Surface.  The  deeply 
grooved  single  root  is  not  quite  complete,  and  shows  the  funnel-shaped  opening  at  the 


Fig.  73  *  (Par.  94).— Left  Upper  Third  Molar  with  five  roots. 


*  Illustration,  IJ^  diameters. 


UPPEK   THIRD   MOLAR.  75 

are  properly  three-cusped  teeth  in  which  the  oblique  ridge 
becomes  the  distal  marginal  ridge,  and  the  distal  groove  runs 
over  to  the  distal  surface  (Fig.  70).  In  the  remainder,  there 
is  only  an  irregular  ridge  (Fig.  71),  forming  a  central  fossa, 
so  marked  with  wrinkles  or  supplemental  grooves  that  the 
developmental  lines  are  not  satisfactorily  made  out.  Many 
examples  of  the  three-cusped  teeth  show  much  relative  dimi- 
nution of  the  disto-buccal  lobe. 

92.  The  upper  third  molar  is  the  smallest  of  the  mo- 
lars,* and  is  more  irregular  in  its  size  and  conformation  than 
the  first  or  the  second  molar.  On  account  of  the  small 
size  of  the  disto-lingual  lobe,  the  distal  portion  of  the  tooth 
is  much  smaller  than  the  mesial,  and  in  the  three-cusped 
teeth  the  crown  becomes  triangular,  with  its  angles  well 
rounded. 

93.  The  mesial  surface  resembles  that  in  the  upper  first 
and  second  molars,  but  is  more  rounded,  so  that  a  concave 
portion  is  less  frequent,  and  the  distal  surface  is  well  rounded. 
The  lingual  and  buccal  surfaces  are  more  rounded  than  the 
same  surfaces  in  the  other  upper  molars.  The  gingival  line 
is  usually  horizontal  in  its  course  around  the  neck  of  the 
tooth,  except  that,  in  a  few  examples,  there  is  a  slight  curv- 
ature on  the  mesial  surface.  Many  upper  third  molars  are 
much  flattened  from  mesial  to  distal.  These  generally  have 
a  considerable  concavity  on  the  mesial  surface.  Occasionally 
teeth  are  found  that  are  also  abnormally  small  and  have  the 
appearance  of  supernumeraries.  More  rarely  this  tooth  fails 
to  develop,  and  is  wanting  entirely. 

94.  The  root  of  the  upper  third  molar  has,  in  the  more 
regular  forms,  the  three  divisions  common  to  the  upper  mo- 
lars, though  relatively  smaller  and  not  so  widely  separated  as 
those  of  the  first  and  second  molars  ;  and  often  end  in  slender 
conical  points  ;  many  have  but  a  single  root ;  but  in  most  of 


*  Forty  upper  first  molars  balanced  sixty  upper  third  molais. 


76  THE    LOWER   MOLARS LOWER    FIRST    MOLAR. 

these  the  three  roots  are  outlined  by  grooves  of  more  or  less 
depth  (Fig.  72).  A  considerable  number  have  more  than 
three  roots,  which  are  irregular  in  size  or  form  (Fig.  73). 
Four,  five,  six,  and  even  seven  or  eight  divisions  are  some- 
times met.  The  neck  is  then  generally  broad  from  buccal  to 
lingual,  and  the  occluding  surface  of  the  crown  irregularly 
formed.  Many  of  the  three  casped  teeth  have  the  root  with- 
out divisions. 

THE    LOWER   MOLARS. 

95.  The  lower  molars  differ  so  much  from  each  other, 
especially  the  first  and  second,  that  each  must  be  separately 
described. 

THE    LOWER    EIRST    MOLAR. 

96.  The  lower  first  molar  is  the  sixth  tooth  from  the 
median  line  in  the  lower  jaw.  It  proximates  the  lower  second 
bicuspid  with  its  mesial  surface,  and  the  lower  second  molar 
with  its  distal.  I^ext  to  the  upper  first  molar,  it  is  the  larg- 
est tooth  in  the  denture.*  The  outline  of  the  occluding  sur- 
face (Figs.  74  and  75),  when  seen  in  a  line  with  the  long  axis 
of  the  tooth,  is  trapezodial,  with  the  buccal  line  the  longer. 
The  buccal  angles  are  about  equally  acute,  while  the  lingual 
angles  are  equally  obtuse,  and  all  are  more  or  less  rounded. 
The  buccal  margin  is  convex,  but  made  irregular  by  two 
buccal  grooves.  The  lingual  angle  is  nearly  straight,  but 
sometimes  slightly  concave,  or  notched  in  the  center  of  its 
length,  by  the  lingual  groove ;  but  more  generally  it  is 
slightly  convex.  The  mesial  and  the  distal  lines  are  nearly 
straight  in  the  best  formed  teeth  ;  though  the  distal  is  some- 
times considerably  convex,  as  the  fifth,  or  disto-lingaal  cusp 
is  more  or  less  prominent.  All  of  these  lines  vary  very  much 
as  to  their  convexity  ;  the  rule  being  that,  in  teeth  of  large 
size  and  symmetrical  development,  they  approach  nearer  to 
straight  lines. 

*  Forty-two  upper  first  molars  balanced  forty-six  lower  first  molars. 


Fig.  77. 


Fig.  74*  (Par.  96).— Left  Lower  First  Molar,  Occluding  Surface,  of  typical  form. 
a,  Mesio-buccal  cusp ;  b,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ; 
e,  distal  cusp ;  /,  mesial  marginal  ridge ;  g,  distal  marginal  ridge ;  h,  mesio-buccal  tri- 
angular ridge ;  i,  disto-buccal  triangular  ridge ;  k,  disto-lingual  triangular  ridge ;  I, 
mesio-lingual  triangular  ridge ;  vi,  distal  triangular  ridge ;  n,  mesial  groove ;  o,  buccal 
groove ;  p,  disto-buccal  groove ;  r,  distal  groove ;  s,  lingual  groove. 

Fig.  75*  (Par.  96).— Right  Lower  First  Molar,  Occluding  Surface,  a,  Mesio-buccal 
cusp ;  6,  disto-buccal  cusp ;  c,  mesial  lingual  cusp ;  d,  disto-lingual  cusp ;  e,  distal  cusp ; 
/,  mesial  marginal  ridge ;  g,  distal  marginal  ridge  ;  h,  mesial  triangular  ridge ;  i,  disto- 
buccal  triangular  ridge ;  k,  mesio-lingual  triangular  ridge ;  I,  disto-lingual  triangular 
ridge ;  11,  mesial  groove  ;  0,  buccal  groove ;  p,  disto-buccal  groove ;  r,  distal  groove ;  s, 
lingual  groove ;  t,  mesio-buccal  triangular  groove. 

Fig.  76*  (Par.  104).— Left  Lower  First  Molar,  Buccal  Surface,  a,  Mesio-buccal 
cusp ;  6,  disto-buccal  cusp ;  c,  distal  cusp ;  d,  bucco-gingival  ridge ;  e,  buccal  pit ;  /, 
gingival  line ;  g,  mesial  root ;  h,  distal  root ;  i,  buccal  groove ;  k,  disto-buccal  groove. 

Fig.  77*  (Par.  104).— Left  Lower  First  Molar,  Buccal  Surface,  with  prominent 
cusps.    References  the  same  as  for  Fig.  76. 


*  Illustration,  ly^  diameters. 


LOWER   FIRST   MOLAR.  79 

97.  Each  of  these  marginal  portions  is  surmounted  by 
the  mesial,  buccal,  lingual,  and  distal  marginal  ridges,  which 
form  a  continuous  elevation  of  irregular  height  around  the 
margins  of  the  occluding  surface,  and  on  which  there  are  five 
cusps.  The  central  inclinations  of  these  ridges  forms  the 
central  fossa.  On  the  mesial,  lingual,  and  distal,  the  sum- 
mits of  these  ridges  are  closed  on  the  margins  of  the  surface ; 
but  on  the  buccal,  there  is  an  inward  inclination  of  the  buc- 
cal surface  that  carries  the  summit  of  the  ridge  considerably 
toward  the  central  axis  of  the  tooth. 

98.  The  occluding  surface  has  five  develojpmental 
grooves  (Figs.  74  and  75) — the  mesial,  buccal,  disto-buccal, 
lingual,  and  distal — which  divide  it  into  five  developmental 
parts,  or  lobes.  These  are  the  mesio-buccal  (a),  disto-buccal 
(b),  mesio-lingual  (c),  disto-lingual  (d),  and  distal  (e)  lobes ; 
each  bearing  a  cusp  of  the  same  name.  The  mesial  grove 
(n)  runs  from  the  central  fossa  over  the  mesial  marginal  ridge 
to  the  mesial  surface.  On  the  mesial  marginal  ridge  it  is 
usually  a  fine  line  which  is  soon  obliterated  by  wear.  Oc- 
casionally, this  is  divided  into  two  branches,  with  a  small 
tubercle  on  the  mesial  marginal  ridge  between  them  (Fig.  74, 
/).  In  many  examples  there  is  a  supplemental  groove  which 
rises  from  the  mesial  groove  at  about  the  center  of  its  length, 
and  runs  toward  the  mesio-buccal  angle.  This  is  the  mesio- 
buccal  triangular  groove  (Fig.  75,  t).  It  divides  the  mesial 
marginal  ridge  from  the  triangular  ridge  of  the  mesio-buccal 
cusp.  More  rarely  there  is  also  a  similar  groove  running  to- 
ward the  mesio-lingual  cusp.  "When  these  are  deep,  they 
form  a  mesial  supplemental  fossa  (Fig.  75,  t).  The  buccal 
groove  (o)  runs  in  a  deep  sulcus  from  the  central  pit  to,  and 
over,  the  buccal  marginal  ridge  to  the  buccal  surface,  and 
divides  the  mesio-buccal  from  the  disto-buccal  cusp.  The 
disto-buccal  groove  (p)  also  runs  from  the  central  pit  over 
the  buccal  ridge,  more  or  less  near  the  distal  angle,  as  the 
distal  cusp  is  large  or  small.     It  divides  the  disto-buccal  lobe 


80  LOWER    FIRST    MOLAR. 


from  the  distal.  The  luigual  grooves  (s)  runs  from  the  cen- 
tral pit  in  a  deep  sulcus  to,  and  over,  the  lingual  marginal 
ridge  onto  the  lingual  surface,  and  divides  the  two  lingual 
lobes.  The  distal  groove  (z*)  runs  distallj  over  the  distal 
marginal  ridge,  and  divides  the  clisto-lingual  lobe  from  the 
distal.  Frequently  this  groove  can  be  traced  some  distance 
toward  the  gingival  line  on  the  distal  surface.  The  mesial 
and  distal  grooves  form  a  line  traversing  the  whole  extent 
of  the  occluding  surface,  from  mesial  to  distal,  in  the  center 
of  which  a  V-sb^P^^l  deflection  is  formed  with  its  point  to 
the  lingual,  the  base  receiving  the  point  of  the  triangular 
ridge  {i)  of  the  disto-buccal  cusp. 

99.  In  most  examples,  the  central  fossa  occupies  all  the 
occluding  surface  within  the  circle  of  the  summit  of  the  mar- 
ginal ridges,  though,  occasionally,  one  or  more  supplemental 
fossse  are  divided  from  it  by  high  triangular  ridges  running 
down  from  the  cusps  (Fig.  75,  A,  k).  The  surface  of  the  fossa 
is  made  irregular  in  most  of  these  teeth  by  deep  sulci  on 
the  lines  of  the  grooves,  separating  the  cusps  and  triangular 
ridges. 

100.  The  occluding  surface  of  the  lower  first  molar  has 
five  cusps,  one  on  each  of  the  five  lobes,  or  three  on  the  buccal 
marginal,  and  two  on  the  lingual  marginal  ridge.-"  These 
cusps  are  formed  by  the  grooves  previously  described  (98), 
which  pass  over  the  ridges  in  depressions  of  variable  depth, 
thus  subdividing  the  crests  of  the  ridges  into  obtuse  eleva- 
tions. Usually,  these  are  not  so  high  and  prominent  as  the 
cusps  of  the  upper  molars.  The  mesio-buccal  (Figs.  74  and  75, 
a)  is  the  largest  and  strongest  of  the  buccal  cusps,  and  occupies 
rather  more  than  one-third  of  the  buccal  marginal  ridge. 
From  its  crest  a  triangular  ridge  (A)  runs  down  centrally  to 
the  junction  of  the  mesial  and  buccal  grooves,  and  is  divided 
from  a  similar  triangular  ridge  from  the  mesio-lingual  cusp, 

*  In  some  rare  cases  lower  first  molars  have  but  four  cusps,  and  then  the 
tooth  is  like  the  lower  second  molar  (109,  110). 


LOAVER    FIRST    MOLAR.  81 

by  the  mesial  groove.  When  these  two  ridges  are  high,  they 
form,  in  conjunction  with  triangular  grooves  between  them 
and  the  mesial  marginal  ridge,  a  mesial  supplemental  fossa. 
The  disto-buccal  cusp  [b)  is  of  less  extent  from  mesial  ta 
distal,  but  has  a  longer  triangular  ridge,  though  not  so  high, 
which  ends  in  the  point  of  the  V-shaped  deflection  of  the- 
mesial  and  distal  grooves,  or  at  their  junction. 

101.  The  lingual  cusps  (c,  d)  are  about  equal  in  size 
and  height  (perhaps  the  mesial  is  a  little  the  higher  on  the 
average).  Each  has  strong  triangular  ridges  {k,l)  which 
terminate  in  the  angles  formed  by  the  junction  of  the  lingual 
groove  with  the  mesial  and  distal  grooves  in  the  central  pit. 

102.  The  distal  cusp  {e)  occupies  the  distal  portion  of 
the  buccal  ridge,  and  forms  the  disto-buccal  angle  of  the 
tooth.  It  is  the  distinguishing  mark  of  the  lower  first 
molar,  being  but  very  rarely  absent  in  that  tooth,  and  never 
present  in  the  lower  second  molar.  It  is  the  smallest  of  the 
five  cusps,  and  varies  most  in  its  relative  size.  In  some  ex- 
amples it  is  almost  or  quite  as  large  as  the  disto-buccal  cusp. 
In  others,  especially  in  small  and  poorly  developed  teeth,  it 
may  be  reduced  to  a  mere  tubercle,  occupying  the  buccal 
portion  of  the  distal  marginal  ridge  and  the  immediate 
disto-buccal  angle.  The  triangular  ridge,  or  central  incline, 
of  this  cusp  is  commonly  nearly  fiat,  but  occasionally  has  a 
rounded  crest.  It  ends  in  a  point  at  the  junction  of  the 
distal  and  disto-buccal  grooves. 

1 03.  In  this  tooth  there  is  often  a  deep  pit  at  the  junc- 
tion of  the  mesial,  distal,  and  lingual  grooves.  Less  fre- 
quently there  is  also  a  pit  at  the  junction  of  the  mesial  and 
buccal  grooves,  and  at  the  junction  of  the  distal  and  disto- 
buccal  grooves.  The  grooves  are  often  fissured  for  a  short 
distance  from  the  pits,  especially  in  the  deeply  sulcate  lingual 
groove.  In  some  very  poorly  developed  teeth  fissures  may 
be  found  in  any  part  of  the  grooves. 

104.  The  buccal  surface  of  the  lower  first  molar  (Figs. 


S2  LOWER    FIRST    MOLAR. 


76  and  77),  when  seen  at  right  angles  with  the  long  axis  of  the 
tooth,  is  irregularly  trapezoid  in  form,  with  the  occluding 
margin  about  two-sevenths  longer  than  the  gingival.  The 
mesial  and  distal  margins  converge  toward  the  gingival, 
and  their  angles,  with  the  occluding  surface,  are  about 
■equally  acute.  The  occluding  margin  is  broken  into  three 
elevations,  or  cusps,  by  the  buccal  and  disto-buccal  grooves. 
The  gingival  line  is  straight,  or  slightly  curved,  with  the 
concavity  toward  the  occluding  surface.  The  mesial  and  the 
distal  lines  are  slightly  convex.  The  buccal  surface  is  con- 
vex in  all  directions ;  but  the  line  of  convexity  from  mesial 
to  distal  is  broken  toward  the  occluding  margin  by  the 
buccal  and  disto-buccal  grooves,  which  pass  over  from  the 
occluding  surface.  The  buccal  groove  (z)  is  usually  a  little 
to  the  mesial  of  the  central  line  of  the  surface,  and  often  ends 
in  a  deep  pit  (e),  about  half  way  from  the  occluding  to  the 
gingival  margin.  Exceptionally,  this  groove  is  continued 
to  the  bifurcation  of  the  root.  The  disto-buccal  groove  (k) 
is  near  the  disto-buccal  angle,  and  its  course  is  toward  the 
gingival  line,  with  a  distal  inclination.  It  is  usually  lost  to 
sio-ht  by  becoming  shallower,  but  in  some  examples  it  may 
be  traced  to  the  gingival  line.  The  enamel  terminates  in  a 
marked  inclination  to  the  gingival  line,  forming  the  bucco- 
gingival  ridge. 

105.  The  lingual  surface  of  this  tooth  (Figs.  78  and  79) 
is  slightly  convex  in  all  directions.  It  forms  a  fairly  sharp 
angle  with  the  occluding  surface,  but  is  rounded  away 
toward  the  mesial  and  distal  surfaces.  On  account  of  the 
lino-ual  convergence  of  the  mesial  and  distal  surfaces,  the 
lingual  surface  is  much  shorter  from  the  mesial  to  distal 
than  the  buccal.  The  occluding  margin  is  deeply  notched 
by  the  passage  of  the  lingual  groove  (z),  which  usually  termi- 
nates near  the  center  of  the  surface  by  becoming  shallower. 

106.  The  mesial  surface  (Fig.  80)  is  ver}^  irregular  in 
■outline,  and  often  the  occluding  margin  is   deeply  concave. 


Fig.  78. 


Fig.  79. 


Fig.  81. 


Fig.  82 


Fig.  78*  (Par.  105).— Left  Lower  First  Molar,  Lingual  Surface,  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp ;  c,  distal  cusp ;  d,  mesio-lingual  cusp ;  e,  disto-lingual  cusp ; 
/,  /,  gingival  line ;  g,  mesial  root ;  h,  distal  root.  The  roots  are  spread  wide  apart ; 
i,  lingual  groove. 

Fig.  79*  (Par.  105).— Left  Lower  First  Molar,  Lingual  Surface.  This  tooth  has 
prominent  cusps,  and  the  roots  are  straight  and  close  together.  References  the  same  as 
for  Fig.  78. 

Fig.  80*  (Par.  106). — Left  Lower  First  Molar,  Mesial  Surface,  a,  Mesio-buccal 
cusp ;  d,  mesio-Ungual  cusp ;  e,  mesial  surface,  point  of  concavity ;  /,  /,  gingival  line ; 
g,  mesial  root  with  broad  groove. 

Fig.  81*  (Par.  107). — Left  Lower  First  Molar,  Distal  Surface.  The  cusps  are 
very  prominent,  a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  distal  cusp ;  d,  mesio- 
lingual  cusp ;  e,  disto-lingual  cusp ;  /,  gingival  line ;  g,  mesial  root ;  h,  distal  root. 

Fig.  82  *  (Par.  108).— Lower  First  Molar,  with  three  roots. 


*  Illustration,  1}^  diameters. 


LOWER   FIRST   MOLAR.  85 

The  gingival  curvature  is  generally  marked,  and  the  buccal 
and  lingual  lines  convex.  The  buccal  line  is  more  convex 
than  the  lingual,  and  its  curvature  is  at  such  an  incline  as 
to  render  the  gingival  line  much  longer  than  the  occluding 
margin.  The  surface  is  slightly  convex,  though  almost  j&at ; 
but,  in  the  central  portion,  near  the  gingival  line,  it  is  some- 
times slightly  concave  from  buccal  to  lingual.  It  is  rounded 
away  toward  the  labial  and  lingual  angles.  With  the  occlud- 
ing surface  it  forms  a  sharp  angle  in  the  central  portion,  but 
is  rounded  toward  the  buccal  and  lingual  angles.  In  the  di- 
rection of  the  long  axis  of  the  tooth,  there  is  usually  a  con- 
cavity at  the  junction  of  the  enamel  and  cementum. 

107.  The  distal  surface  (Fig.  81)  is  smoothly  convex 
from  buccal  to  lingual.  From  the  occluding  surface  to  the 
gingival  line  it  is  straight  or  slightly  convex,  but  forms  a 
considerable  concavity  at  the  junction  of  the  crown  with  the 
root,  which  occasionally  forms  a  sharp  angle,  but  generally 
is  well  rounded.  The  occluding  margin  is  often  deeply 
notched  by  the  distal  groove.  In  a  few  examples  the  disto- 
buccal  groove  is  deep  after  passing  over  the  marginal  ridge, 
and  in  its  distal  inclination  forms  a  slight  concavity  at  the 
disto-buccal  angle. 

108.  The  root  of  the  lower  first  molar  is  divided  into 
two  prongs  (Figs.  76  to  82),  and  this  division  is  usually  close 
to  the  crown,  closer  than  in  any  other  tooth  in  the  mouth. 
The  mesial  root  {g)  inclines  first  to  the  mesial,  and  then 
curves  regularly  toward  the  distal.  It  is  broad  from  buccal 
to  lingual,  and  is  much  thinned  from  mesial  to  distal,  so  that 
in  cross  sections  it  measures  double  as  much  one  way  as  the 
other.  It  is  usually  slightly  concave  on  both  mesial  and  dis- 
tal surfaces,  and  tapers  regularly,  but  not  rapidly,  from  the 
bifurcation  to  the  apex,  and  ends  in  a  flattened,  but  well 
rounded,  point.  The  distal  root  (A)  inclines  to  the  distal  at 
first,  and  afterward  is  nearly  or  quite  straight.  In  some  ex- 
amples the  apical  half,  curves  to  the  distal,  but  more  often 


86  LOWER    SECOND   MOLAR. 

toward  the  mesial,  so  that  the  apexes  of  the  two  roots  are 
inclined  toward  each  other.  It  is  narrower  from  buccal  to 
lingual  than  the  mesial  root,  and  more  nearly  round,  being 
but  rarely  concave  or  grooved  on  either  mesial  or  distal  sur- 
face. It  tapers  quite  regularly,  and  more  nearly  to  a  point 
than  the  mesial  root,  though  the  apex  is  generally  well 
rounded.  -  The  form  of  the  root  is  regular,  rarely  deviating 
much  from  its  type.  Occasionally,  however,  the  division  of 
the  root  is  incomplete.  The  mesial  root  is  occasionally  di- 
vided, giving  the  tooth  three  roots  (Fig.  82);  and  I  have 
seen  a  few  in  which  the  distal  root  was  divided  also,  giving 
four  roots. 

THE    LOWER    SECOND    MOLAR. 

109.  The  most  characteristic  difference  between  the 
lower  first  and  second  molars  is  the  absence  of  the  fifth  lobe 
in  the  second,  and  the  general  change  of  form  which  this 
absence  implies ;  the  other  parts  of  the  tooth  being  similar, 

110.  When  the  occluding  surface  is  seen  in  a  line  with 
the  long  axis  of  the  tooth  (Fig.  83),  the  outline  of  the  crown 
is  nearly  a  parallelogram,  with  angles  rounded  and  the  lines 
slightly  convex,  the  buccal  most.  The  summits  of  the  mar- 
ginal ridges  are  close  on  the  mesial,  distal,  and  lingual 
margins,  while  the  buccal  is  carried  over  toward  the  lingual 
by  the  inclination  of  the  buccal  surface.  The  central  inclines 
of  the  marginal  ridges  form  a  deep  central  fossa,  in  the  cen- 
ter of  which  there  is  usually  a  deep  pit. 

111.  There  are  four  developmental  grooves,  all  arising 
from  the  central  pit.  The  mesial  groove  (l)  runs  to  the  me- 
sial margin  and  crosses  the  mesial  marginal  ridge  as  a  fine 
line,  which  is  often  obliterated  by  wear.  The  distal  groove 
(o)  runs  in  a  similar  way  to  the  distal  surface.  These  two 
grooves  divide  the  occluding  surface  from  mesial  to  distal, 
and  centrally,  between  the  summits  of  the  buccal  andlingual 
marginal  ridges.  The  buccal  groove  (m)  runs  from  the  cen- 
tral pit  to   the  buccal  margin,  and  over  it  to  the  buccal 


Fig.  83. 


Fig.  85. 


Fig.  86. 


Fig.  87 


Fig.  88. 


Fig.  89. 


Fig.  83  *  (Par.  110).— Right  Lower  Second  Molae,  Occluding  Surface,  of  typical 
form,  o,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp ;  d,  disto-lingual 
cusp  ;  e,  mesial  marginal  ridge  ;  /,  distal  marginal  ridge  ;  g,  mesio-buccal  triangular  ridge ; 
h,  disto-buccal  triangular  ridge  ;  i,  mesio-lingual  triangular  ridge  ;  k,  disto-lingual  trian- 
gular ridge  ;  I,  mesial  groove  ;  m,  buccal  groove  ;  n,  lingual  groove  ;  o,  distal  groove. 

Fig.  84*  (Par.  113).— Right  Lower  Second  Molar,  Occluding  Surface,  of  imperfect 
form,  a,  Mesio-buccal  cusp ;  b,  disto-buccal  cusp ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual 
cusp  ;  e,  mesial  marginal  ridge  ;  /,  distal  marginal  ridge ;  g,  mesio-buccal  triangular  ridge ; 
h,  disto-buccal  triangular  ridge  ;  i,  mesio-lingual  triangular  ridge  ;  k,  disto-lingual  trian- 
gular ridge  ;  I,  mesial  groove  ;  to,  buccal  groove  ;  n,  lingual  groove  ;  o,  distal  groove. 

Fig.  85  *  (Par.  115).— Left  Lower  Second  Molar,  Buccal  Surface,  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp  ;  c,  buccal  groove ;  d,  buccal  pit ;  /,  gingival  line ;  g,  mesial 
root ;  h,  distal  root. 

Fig.  86  *  (Par.  116).— Left  Lower  Second  Molar,  Lingual  Surface,  a,  Mesio-buccal 
cusp ;  b,  disto-buccal  cusp ;  c,  mesio-lingual  cusp  ;  d,  disto-lingual  cusp ;  e,  lingual  groove ; 
/,  gingival  line ;  g,  mesial  root ;  h,  distal  root. 

Fig.  87  *  (Par.  117).— Left  Lower  Second  Molar,  Mesial  Surface,  a,  Mesio-buccal 
cusp ;  c,  mesio-lingual  cusp ;  d,  point  of  proximate  contact  of  mesial  surface  ;  /,  gingival 
line ;  g,  mesial  root. 

Fig.  88*  (Par.  118).— Left  Lower  Second  Molar,  Distal  Surface,  o,  Mesio-buccal 
cusp ;  6,  disto-buccal  cusp  ;  c,  mesio-lingual  cusp ;  d,  disto-lingual  cusp ;  e,  point  of  proxi- 
mate contact  of  the  distal  surface ;  /,  gingival  line  ;  h,  distal  root. 

Fig.  89*  (Par.  119).— Right  Lower  Second  Molar,  Lingual  Surface.  The  roots 
are  curved  very  much  to  the  distal. 

*  Illustration,  IJ^  diameters. 


LOWER    SECOND   MOLAR.  89 


surface,  dividing  the  buccal  ridge  into  two  buccal  cusps,  while 
the  lingual  {n)  runs  to  and  over  the  lingual  marginal 
ridge,  dividing  it  also  into  two  lingual  cusps.  The  two 
divide  the  tooth  from  buccal  to  lingual,  into  nearly  equal 
parts.  The  mesial  j^ortion  is  usually  slightly  the  larger. 
The  four  grooves  form  a  cross  through  the  occluding  sur- 
face, dividing  it  into  four  lobes,  or  developmental  parts,  on 
each  of  which  there  is  a  cusp  and  a  triangular  ridge.  In 
some  examples  the  grooves  do  not  exactly  meet  at  the  cen- 
tral pit.  The  central  may  rise  to  the  mesial  of  the  buccal, 
or  vice  versa;  or,  a  similar  variation  may  occur  in  the  central 
ends  of  the  mesial  and  distal,  causing  irregularity  of  the 
contour  of  the  central  fossa.  Occasionally,  the  lobes  are  of 
unequal  size,  or  the  cusps  are  unequally  developed,  giving 
rise  to  imperfect  forms  (Fig.  84). 

112.  On  the  average,  the  cusps  of  the  second  lower 
molar  are  higher  and  more  pointed,  and  the  triangular  ridges 
are  more  prominent  than  in  the  first  molar.  The  mesio-buc- 
cal  and  mesio-lingual  cusps  are  generally  a  little  larger  than 
the  disto-buccal  and  disto-lingual ;  also,  the  mesio-buccal 
and  mesio-lingual  triangular  ridges  (Fig.  83,  g,  i)  are  usu- 
ally more  prominent.  The  crests  of  these  ridges  do  not  run 
directly  toward  the  central  pit,  but  the  two  mesial  ones  meet 
raesially  of  the  central  pit,  while  the  two  distal  meet  distally 
of  it.  When  they  are  high,  they  form  transverse  ridges  by 
their  junction,  which  separate  a  mesial  and  a  distal  supple- 
mental fossa  from  the  central  fossa.  When  this  occurs,  there 
are  usually  triangular  supplemental  grooves  deflected  from 
the  mesial  and  distal  grooves,  to  the  mesial  and  distal  of  the 
triangular  ridges,  which  run  towards  the  angles  of  the  tooth 
and  separate  the  triangular  from  the  marginal  ridges,  widen- 
ing and  deepening  the  supplemental  fossae.  A  deep  pit  is 
often  found  at  the  point  where  these  triangular  grooves 
arise  from  the  principal  grooves.  Supplemental  fossae  occur 
much  more  frequently,  or  are  more  pronounced,  in  the  mesial 


90  LOWER   SECOND   MOLAR. 

than  ill  the  distal  portion  of  the  tooth,  but  in  many  exam- 
ples the  triaDgular  ridges  are  so  widely  divided  by  sulcate^ 
mesial  and  distal  grooves  that  no  supplemental  fossse  are  seen. 

113.  In  some  examples  the  lower  second  molar  presents 
differences  in  the  comparative  size  of  its  lobes,  and  the 
grooves  may  be  deflected  from  their  normal  course.  Occa- 
sionally, the  distal  groove  is  divided,  and  passes  over  the  dis- 
tal marginal  ridge  in  two  divisions,  with  a  small  tubercle 
between  them.  In  poorly  developed  teeth  there  may  be 
many  supplemental  grooves,  or  wrinkles,  running  from  the 
developmental  grooves  up  onto  the  central  inclines  of  the 
ridges  and  cusps. 

114.  Fissures  occur  oftenest  near  the  central  ends  of 
the  grooves ;  though  they  ma}^  appear  in  any  part  of  their 
length;  and  in  poorly  developed  teeth  the  supplemental 
grooves  may  be  deeply  fissured. 

115.  The  buccal  surface  of  the  lower  second  molar 
(Fig.  85)  is  convex  in  all  directions,  except  that  it  is  partially 
divided  into  two  sections,  or  ridges,  by  the  buccal  groove  (c),. 
which  runs  over  onto  it  from  the  occluding  surface.  In 
many,  this  groove  ends  near  the  center  of  the  surface  in  a 
deep  buccal  pit  {d).  This  tooth  has  no  disto-buccal  groove. 
The  mesial  and  distal  margins  converge  less  toward  the 
gingival  line  than  it  does  in  the  lower  first  molar.  The 
gingival  line  is  nearly  straight,  and  there  is  a  strong  inclina- 
tion of  the  border  of  the  enamel  toward  it,  giving  the  ap- 
pearance of  a  gingival  enamel  ridge. 

116.  The  lingual  surface  (Fig.  86)  is  similar  in  all 
points  to  that  of  the  lower  first  molar  (g.  v.,  105);  but,  on 
account  of  a  much  less  convergence  of  the  mesial  and  distal 
surfaces  toward  the  lingual,  this  surface  is  nearly  as  great  as 
the  buccal  surface. 

117.  The  mesial  surface  (Fig.  87)  of  the  lower  second 
molar  is  generally  a  little  more  convex  than  in  the  lower 
first  {q.  v.,  106) ;  but  in  other  respects  they  are  similar. 


LOWER   THIRD  MOLAR.  91 

118.  The  distal  surface  (Fig.  88)  difters  from  that  of 
the  lower  first  molar  in  not  having  the  distal  protuberance 
of  the  fifth  cusp.  Its  proximating  point  with  the  tooth 
distal  to  it  is  usually  central,  or  toward  the  lingual,  instead 
of  the  buccal  angle,  as  in  the  lower  first  molar.  This  surface 
is  usually  quite  regularly,  and  smoothly,  convex,  and  its 
gingival  line  seldom  shows  any  bucco-lingual  curvature. 

119.  The  roots  of  the  lower  second  molar  (Figs.  85  to 
89)  are  similar  to  those  of  the  first  molar;  but  the  divisions 
are  much  less  spread  and  less  grooved  on  the  mesial  and 
distal  sides.  In  many  examples  there  is  but  a  single  root^ 
which  is  deeply  grooved  on  its  buccal  and  distal  sides,  mark- 
ing out  the  divisions.  The  root  is  much  more  irregular  in 
form  than  in  the  lower  first  molar,  and  is  often  much  curved 
distally  (Fig.  89)  or  otherwise  distorted. 

THE  LOWER  THIRD  MOLAR. 

120.  The  lower  third  molar,  called  also  the  wisdom 
tooth  and  dens  sapientia,  is  the  eighth  from  the  median  line, 
and  the  last  tooth  in  the  arch.  It  proximates  the  lower 
second  molar  by  its  mesial  surface.  The  tooth  has  two 
typical  forms ;  the  one  is  a  four-cusped  tooth,  similar  to  the 
lower  second  molar  (Fig.  83) ;  the  other  a  five-cusped  tooth, 
similar  to  the  lower  first  molar  (Fig.  75) ;  but  there  are 
great  variations  from  both  of  these.  Indeed,  within  the 
observation  of  the  author  the  form  of  this  tooth  is  oftener 
distorted  than  any  other. 

121.  The  four-lobed  tooth  is  the  more  common  form, 
and,  when  well  developed,  the  occluding  surface  is  similar  to 
that  of  the  lower  second  molar.  A  supplemental  fossa  is 
often  seen,  formed  by  the  prominence  of  the  mesio-buccal 
and  mesio-lingual  triangular  ridges  ;  but  in  the  distal  portion 
of  the  crown  such  a  fossa  rarely  appears.  Indeed,  in  the 
four-cusped  lower  third  molars,  the  distal  lobes  are  generally 
much  smaller  than  the  mesial  lobes. 


92  LOWER    THIRD    MOLAR. 


122.  The  course  of  the  grooves  is  often  much  distorted, 
so  that  their  central  ends  fail  to  proximate,  as  in  Fig.  90, 
or  otherwise.  This  renders  the  form  of  the  central  fossa 
extremely  irregular.  Or  the  principal  grooves  may  be  so 
confused  among  a  number  of  supplemental  grooves  that  the 
real  dividing  lines  of  the  lobes  can  scarcely  be  made  out 
(Fig.  91).  In  many  of  these,  some  of  the  supplemental 
grooves  run  over  the  marginal  ridges,  corrugating  them,  or 
dividing  them  into  several  imperfect  cusps.  Occasionally 
the  marginal  ridges  are  nearly  equal  in  height  all  around  the 
margin  of  the  central  fossa,  and  the  enamel  surface  of  the 
latter  is  covered  with  small  wrinkles,  some  of  which  may  be 
deeply  fissured. 

123.  In  some  instances  the  lower  third  molar  is  very 
large,  and  in  these  the  ridges  may  be  subdivided  into  six, 
seven,  or  eight  cusps,  and  as  many  fairly  distinct  lobes ;  or, 
one  or  more  supplemental  ridges  may  appear  within  the 
limits  of  the  central  fossa  surrounded  by  grooves,  which 
divide  them  from  other  parts  of  the  crown  (Fig.  92).  Such 
teeth  are  usually  poorly  formed,  and  the  grooves  deeply 
fissured. 

124.  The  five-lobed  lower  third  molars  are  very  large 
teeth,  larger  than  the  second  molars,  and  very  regularly 
formed.  The  distal  lobe  is  placed  further  to  the  distal  and 
lingual,  and  the  buccal  surface  is  more  rounded  than  in  the 
first  molars.     This  form  is  bilateral  and  hereditary. 

125.  The  buccal  surface  of  the  lower  third  molar  (Figs. 
93,  94,  95)  is  usually  more  convex  than  in  the  other  lower 
molars,  but  otherwise  of  the  same  form.  If  four-lobed,  this 
tooth  has  the  same  grooves  and  pits  as  the  lower  second  ;  if 
five-lobed,  it  has  the  markings  of  the  lower  first  molars. 

126.  The  mesial,  lingual,  and  distal  surfaces  corre- 
spond with  those  of  the  other  lower  molars,  only  rather  more 
rounded  ;  especially  the  distal,  which  is  often  nearly  a  true 
circle  from  buccal  to  lingual. 


(h'  ^„.~u^ 


Fig.  93. 


Fig-.  94. 


Fig.  95. 


Fig.  90*  (Par.  122).— Left  Lower  Third  Molar,  Occluding  Surface,  imperfect 
form,  a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual 
cusp ;  e,  mesial  marginal  ridge ;  /,  distal  marginal  ridge ;  g,  mesial  groove ;  h,  buccal 
groove ;  i,  lingual  groove ;  /:,  distal  groove.  The  buccal  and  lingual  grooves  do  not  meet 
in  the  central  fossa  as  in  regular  forms. 

Fig.  91*  (Par.  122). — Lower  Third  Molar,  Occluding  Surface,  very  imperfect 
form,  a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  mesio-lingual  cusp ;  d,  disto-lingual 
cusp ;  e,  mesial  marginal  ridge ;  /,  distal  marginal  ridge ;  g,  mesial  groove ;  h,  buccal 
groove  ;  i,  lingual  groove ;  k,  distal  groove.  Several  of  the  grooves  are  fissured  and  are 
irregular  in  form. 

Fig.  92*  (Par.  12.").— Right  Lower  Third  Molar,  Occluding  Surface,  very  large 
and  irregular  form,  a,  Mesio-buccal  cusp ;  6,  a  very  imperfect  disto-buccal  cusp ;  c, 
mesio-Ungual  cusp,  with  a  sharp,  triangular  ridge,  running  very  much  to  the  distal ;  d, 
disto-lingual  cusp,  standing  very  much  to  the  mesial  of  its  proper  position ;  e,  /,  a  large 
supplemental  ridge,  occupying  the  middle  portion  of  the  central  fossa ;  g,  mesial  margi- 
nal ridge ;  li,  distal  marginal  ridge ;  i,  mesial  groove,  deeply  fissured  and  with  supple- 
mental grooves,  also  fissured,  extending  to  the  labial  and  lingual,  forming  a  supplemental 
mesial  fossa ;  A-,  buccal  groove ;  I,  lingual  groove ;  m,  n,  deep  fissure  on  either  side  of  the 
supplemental  ridge.  There  are  a  number  of  deep  wrinkles  running  over  the  distal  margi- 
nal ridge. 

Fig.  93*  (Par.  12.5).— Right  Lower  Third  Molar,  Buccal  Surface,  with  five 
cusps,  a,  Mesio-buccal  cusp ;  6,  disto-buccal  cusp ;  c,  buccal  groove ;  d,  buccal  pit ;  e, 
disto-buccal  groove ;  /,  distal  cusp ;  g,  gingival  line ;  h,  mesial  root ;  /,  distal  root.  In 
this  tooth  the  lingual  root  is  the  larger,  and  the  two  come  together  at  their  apexes,  both 
of  which  is  unusual. 

Fig.  94*  (Par.  127).— Right  Lower  Third  Molar,  with  the  roots  curved  very  much 
to  the  distal. 

Fig.  95*  (Par.  12").— Left  Lower  Third  Molar,  Buccal  Surface;  three  roots,  a, 
Mesio-buccal  cusp ;  b,  disto-buccal  cusp ;  c,  distal  cusp ;  d,  buccal  groove ;  /,  gingival 
line ;  g,  mesial  root ;  h,  distal  root ;  i,  supernumerary  root. 


=  Illustration,  1}^  diameters. 


THE   DECIDUOUS    TEETH.  95 

127.  The  root  of  the  lower  third  molar  (Figs,  93,  94, 
95),  as  compared  with  its  crown,  is  usually  much  smaller 
than  in  the  other  lower  molars.  It  may  be  single,  or  divided 
into  two  or  more  prongs,  the  tendency  being  to  the  forma- 
tion of  two  roots,  the  same  as  in  the  other  lower  molars  ; 
and  much  the  greater  number  has  the  root  in  this  form, 
though  the  single  root  is  common,  and  three  roots  (the 
mesial  being  again  subdivided)  are  not  rare.  The  root,  or 
roots,  of  this  tooth  usually  curve  distally,  sometimes  very 
much,  and  are  otherwise  distorted.  In  extracting,  this 
incline  of  the  roots  should  be  kept  in  mind. 

THE    DECIDUOUS    TEETH. 

128.  These  are  the  teeth  of  early  childhood,  and  serve 
for  mastication  till  the  maxillary  bones  are  sufficiently  de- 
veloped to  accommodate  the  permanent,  the  larger  teeth  of 
adult  age.  They  are  then  removed  by  absorption  of  their 
roots,  Avhich  allows  their  crowns  to  fall  away.  Hence  they 
are  often  called  temporary  teeth.  The  shedding  process  be- 
gins about  the  seventh  year,  and  is  completed  at  from  the 
twelfth  to  the  fourteenth,  the  succedaneous  teeth  taking  the 
places  of  the  deciduous.  There  are  twenty  deciduous  teeth  ; 
ten  in  each  jaw,  namely  :  Two  central  incisors,  two  lateral  in- 
cisors, two  cuspids,  and  four  molars.  This  may  be  expressed 
by  the  following  formula : 

I  f  C  i  M.  1=20. 

There  are  no  bicuspids  in  the  deciduous  set,  and  therefore  the 
deciduous  first  molars  proximate  directly  with  the  deciduous 
cuspids.  The  bicuspids  of  the  permanent  set  are  succedane- 
ous to  the  deciduous  molars. 

129.  The  incisors  and  cuspids  of  the  deciduous  set  are 
(Figs.  96  to  101)  similar  in  form  and  lobal  construction  with 
their  succedaneous  teeth,  but  the  deciduous  molars  give  place 
to  the  permanent  bicuspids,  which  are  of  very  dissimilar 


96  THE    DECIDUOUS    TEETH. 

pattern.  The  deciduous  second  molars  (Fig.  102,  103),  both 
upper  and  lower  are  of  the  same  form  and  lobal  construction 
as  the  permanent  first  molars.  The  deciduous  first  molars^ 
upper  and  lower,  have  no  similar  teeth  in  the  permanent  set. 
Their  form,  and  the  arrangement  of  their  lobes  are  peculiar 
to  themselves.  Therefore  the  crowns  of  these  will  be  sepa- 
rately described. 

130.  Though  the  crowns  of  the  temporary  teeth,  with 
the  exceptions  named,  are  of  similar  form  and  lobal  construc- 
tion as  the  permanent,  there  are  certain  minor  differences 
which  distinguish  them.  They  are  considerably  smaller  than 
the  corresponding  permanent  teeth.  This  reduction  in  size 
includes  the  whole  tooth,  and  is  such  that  it  leaves  the  gen- 
eral proportions  unchanged,  except  that  the  roots  are  pro- 
portionally longer. 

131.  The  deciduous  teeth  are,  however,  marked  with  a 
much  greater  constriction  at  their  necks.  The  enamel,  in- 
stead of  thinning  away  to  the  gingival  border  as  in  the  per- 
manent teeth,  retains  its  thickness  almost  to  the  gingival 
line  and  terminates  abruptly,  leaving  a  sudden  constriction 
of  the  neck  of  the  tooth.  This  varies  in  degree,  but  is  com- 
mon to  all  of  the  deciduous  teeth,  and  distinguishes  them 
from  the  permanent  teeth, 

132.  The  buccal  and  lingual  surfaces  of  the  deciduous 
molars  slope  inward  toward  the  occluding  surface  much  more 
than  those  of  the  permanent,  so  that  the  immediate  occlud- 
ing surface,  is  narrower  in  proportion  to  the  greatest  labio- 
lingual  thickness  of  the  crown.  This  gives  the  crown  as 
seen  in  the  mouth  the  appearance  of  being  very  long  from 
mesial  to  distal ;  though  this  characteristic  is  less  marked  in 
the  upper  than  in  the  lower  deciduous  molars  (see  Figs.  104, 
and  106). 

133.  The  enamel  of  the  deciduous  teeth  is  usually 
whiter  than  the  permanent  teeth,  and  they  are  probably  of 
coarser  texture.   The  difference  in  color  is  often  strongly  con- 


Fig.  96. 


Fiff.  97.  Fig.  98. 


Fig.  99. 


Fig.  100. 


Fig.  101. 


Fig.  107. 


Fig.  103. 


Fig.  106. 


Fig.  104. 


Fig.    96*  (Par.  129).— Deciduous  Upper  Central  Incisor. 

Fig.   97*  (Par.  129).— Deciduous  Upper  Lateral  Incisor. 

Fig.   98*  (Par.  129).— Deciduous  Upper  Cuspid. 

Fig.   99*  (Par.  129).— Deciduous  Lower  Central  Incisor. 

Fig.  100*  (Par.  129).— Deciduous  Lower  Lateral  Incisor. 

Fig.  101*  (Par.  129).— Deciduous  Lower  Cuspid. 

Fig.  102*  (Par.  129).— Left  Upper  Second  Deciduous  Molar. 

Fig.  103*  (Par.  129).— Left  Lower  Second  Deciduous  Molar,  Buccal  Surface. 

Fig.  104*  (Par.  134).— Left  Upper  First  and  Second  Deciduous  Molars.  Tlie  second 
deciduous  molar  has  its  grooves  and  iobes  in  the  same  fonn  as  those  of  the  first  perma- 
nent molar,  Fig.  54.  The  upper  first  deciduous  molar  has  hut  three  cusps,  a,  Mesial 
groove  ;  b,  distal  groove ;  c,  buccal  groove  ;  d,  mesio-buccal  cusp  ;  e,  disto-buccal  cusp ;/, 
lingual  cusp. 

Fig.  105  *  (Par.  138).— Left  Upper  First  Deciduous  Molar,  Buccal  Surface,  a, 
Bucco-gingival  ridge ;  b,  mesio-huccal  cusp ;  c,  disto-buccal  cusp ;  d,  buccal  ridge';  e, 
buccal  groove. 

Fig.  106*  (Par.  141).— Lower  First  and  Second  Deciduous  Molars,  Occluding  Sur- 
faces. The  lobes  and  grooves  of  the  lower  second  deciduous  molar  are  the  same  as  those 
of  the  permanent  lower  first  molar.  Fig.  75.  The  lower  deciduous  first  molar  has  four 
lobes,  a,  Mesial  groove  ;  b,  buccal  groove  ;  c,  lingual  groove  :  d,  distal  groove  ;  e,  mesio- 
buccal  cusp  ;  /,  disto-buccal  cusp  ;  g,  mesio-lingual  cusp  ;  h,  disto-lingual  cusp  ;  i,  'mesial 
fossa. 

Fig.  107*  (Par.  148).— Left  Lower  First  Deciduous  Molar,  Buccal  Surface,  a, 
Bucco-gingival  ridge  ;  6,  mesio-buccal  cusp  ;  c,  disto-buccal  cusp  ;  d,  buccal  ridge";  e, 
buccal  groove. 

*  Illustration,  13^  diameters, 
G 


UPPER   FIRST   DECIDUOUS   MOLAR.  99 

trasted  when  some  of  the  permanent  teeth,  as  the  central  in- 
cisors, have  taken  their  places  hj  the  side  of  the  remaining 
temporary  teeth. 

UPPER    FIRST    DECIDUOUS    MOLAR. 

134.  The  occluding  surface  of  the  upper  first  decidu- 
ous molar  (Fig.  104)  when  seen  in  the  line  of  the  long  axis 
of  the  tooth,  presents  an  irregular  quadrangular  form  in 
which  the  buccal  line  is  the  longer.  The  mesio-buccal  ang-le 
is  acute,  the  mesio-lingual  is  obtuse,  and  both  distal  angles 
are  nearly  right  angles.  The  buccal  margin  is  irregularly 
convex,  and  the  lingual  margin  regularly  rounded.  Both 
the  buccal  and  the  lingual  surfaces  are  much  inclined  cen- 
trally ;  or  toward  the  occluding  surface. 

135.  This  tooth  has  three  lobes,  divided  by  three 
grooves.  The  mesial  (a)  and  distal  {b)  grooves,  run  from  the 
mesial  to  the  distal  margin  in  a  deep  sulcus  and  divide  the 
lingual  from  the  buccal  lobes.  Their  junction  is  in  a  pit  in 
the  central  fossa.  The  buccal  groove  (c)  rises  from  the  same 
pit,  at  the  junction  of  the  mesial  and  distal  grooves,  and 
runs  over  the  buccal  marginal  ridge  to  the  buccal  surface. 
This  groove  is  generally  without  a  sulcus ;  or,  at  most,  there 
is  but  a  slight  furrow. 

136.  The  buccal  marginal  ridge  is  a  high  cutting  edge 
which  rounds  up  from  the  mesio-buccal  angle  and  runs  to 
the  distal  and  buccal  till  it  reaches  the  point  of  the  mesio- 
buccal  cusp  {d).  Its  direction  is  then  to  the  distal,  descend- 
ing slightly  to  the  buccal  groove,  then  horizontally  to  the 
disto-buccal  angle  of  the  tooth  to  join  the  distal  marginal 
ridge,  the  latter  portion  forming  a  small  disto-buccal  cusp  (e). 
In  unworn  teeth,  the  buccal  groove  causes  a  marked  but 
slight  depression  where  it  crosses  the  ridge,  breaking  it  into 
two  cusps ;  the  mesial  being  the  larger  and  more  pointed. 
This  division  is  generally  defaced  very  early  by  wear,  so 
that  the  ridge  presents  an  almost  straight  rounded  edge. 


100  LOWER   FIRST    DECIDUOUS   MOLAR. 

137.  The  lingual  cusp  (/)  is  in  tlie  form  of  an  elevated 
crescentic  edge  with  its  convexity  to  the  lingual,  which  runs 
from  the  mesial  termination  of  the  mesial  groove  {a)  to  the 
distal  terminatin  of  the  distal  groove  (p).  The  central  and  the 
lingual  inclines  of  this  cusp  are  nearly  equal  slopes,  while  the 
buccal  incline  to  the  buccal  marginal  ridge  is  less  abrupt  than 
the  central.  The  mesial  and  distal  marginal  ridges  are  not 
marked  by  more  than  a  very  slight  thickening  of  the  enamel, 
and  are  cut  through  by  the  mesial  and  distal  grooves. 

138.  The  buccal  surface  (Fig.  105)  is  remarkable  for  its 
bucco-gingival  ridge  (a),  which  stands  boldly  out  from  the 
gingival  line  from  one  to  three  millimeters  and  extends  from 
the  mesial  to  the  distal  angle.  At  the  mesio-buccal  angle  it 
terminates  abruptly  in  a  marked  prominence,  and  diminishes 
gradually  as  it  passes  from  the  mesial  to  the  disto-buccal 
angle. 

139.  From  the  summit  of  the  bucco-gingival  ridge  to 
the  summit  of  the  buccal  marginal  ridge,  or  the  mesio-buccal 
cusp,  is  nearly  a  flat  surface,  except  a  slight  depression  along 
the  buccal  groove.  In  many  examples  there  is  a  slight  con- 
cavity extending  from  mesial  to  distal  along  the  occlusive 
margin  of  the  gingival  ridge,  and  from  the  point  of  the 
mesio-buccal  cusp  a  strong  ridge  runs  to  the  mesial  promi- 
nence of  the  gingival  ridge. 

140.  The  mesial  and  distal  surfaces  are  quite  smoothly 
flattened.  The  lingual  surface  is  convex.  The  neck  presents 
the  characteristic  constriction  common  to  deciduous  teeth, 

LOWER   FIRST    DECIDUOUS   MOLAR. 

141.  The  occluding  surface  of  the  lower  first  deciduous 
molar  (Fig.  106),  when  viewed  in  a  line  with  the  long  axis 
of  the  tooth,  presents  the  outline  of  a  parallelogram,  modified 
by  the  rounding  of  its  angles  and  more  or  less  convexity  of 
its  lines.  In  many,  the  distal  portion  of  the  tooth  is  broader 
than  the  mesial,  giving  the  tooth  an  ovoid  outline.     There 


LOWER    FIRST    DECIDUOUS    MOLAR.  101 

are  two  fossse.  The  principal  fossa  occupies  nearl}^  three- 
fourths  of  the  distal  portion  of  the  surface,  while  the  small 
mesial  fossa  occupies  the  immediate  mesial  portion. 

142.  The  tooth  has  four  lobes  of  irregular  form,  divided 
by  four  grooves.  These  grooves  all  run  from  the  principal 
fossa.  The  mesial  groove  (a,  a)  rises  from  the  central  pit  and 
runs  to  the  mesial,  passing  over  the  transverse  ridge  into  the 
mesial  fossa,  where  it  is  deflected  sharply  to  the  lingual, 
passing  over  the  marginal  ridge  near  the  mesio-lingual  angle. 
This  groove  varies  considerably  in  its  course  in  difierent  ex- 
amples. In  the  principal  fossa  it  usually  inclines  to  the 
buccal  and  then  toward  the  lingual,  but  there  is  generally  an 
angle  at  the  origin  of  the  buccal  groove.  The  buccal  groove 
(h)  rises  from  the  mesial  groove,  some  distance  to  the  mesial 
of  the  pit,  and  runs  over  the  buccal  ridge  onto  the  buccal 
surface,  in  a  slight  sulcus,  dividing  the  buccal  marginal  ridge 
into  two  cusps,  the  mesio-  and  disto-buccal.  Its  position  de- 
termines the  relative  size  of  the  buccal  lobes.  The  lingual 
groove  (c)  runs  from  the  central  pit  over  the  lingual  mar- 
ginal ridge  onto  the  lingual  surface,  and  is  deeply  sulcate  on 
the  central  incline  of  the  ridge. 

143.  This  tooth  has  four  cusps  corresponding  with  the 
four  lobes.  The  mesio-buccal  lobe  (e)  is  very  irregular  in  its 
outline.  It  forms  the  entire  mesial  marginal  ridge,  and  from 
one-third  to  three-fourths  of  the  slopes  of  the  mesial  fossa. 
The  mesial  marginal  ridge  is  usually  high  in  young,  unworn, 
teeth.  It  is  curved,  and  from  the  mesio-buccal  angle  it  be- 
comes the  buccal  marginal  ridge,  and  rises  to  the  distal  to 
form  the  point  of  the  mesio-buccal  cusp  (e).  From  the  point 
of  the  cusp  it  falls  away  to  the  distal  and  buccal  to  the 
buccal  groove.  A  prominent  triangular  ridge  descends  from 
this  cusp  to  the  lingual  and  distal,  and  joins  a  similar  tri- 
angular ridge  from  the  mesio-lingual  cusp  {g)  to  form  the 
transverse  ridge,  thus  dividing  the  mesial  from  the  principal 
fossa.     Exceptionally,  a  deep  sulcus  divides  these  triangular 


102  LOWER   FIRST    DECIDUOUS   MOLAR. 

ridges  and  connects  the  fossse.  From  the  buccal  groove,  the 
buccal  marginal  ridge  passes  almost  directly  to  the  disto- 
buccal  angle  where  it  joins  the  distal  marginal  ridge.  In  the 
central  portion  it  rises  slightly  to  form  the  low  disto-buccal 
cusp  (/).  The  triangular  ridge  ftom  this  cusp  is  usually  low, 
or  wanting. 

144.  The  lingual  marginal  ridge  (^,  h)  rises  abruptly 
from  the  mesial  groove  to  the  summit  of  the  mesio-lingual 
cusp  (^),  and  then  falls  away  from  the  distal  and  lingual  to 
the  lingual  groove.  In  most  specimens,  in  unworn  teeth, 
the  mesio-lingual  cusp  is  sharp,  and  its  point  is  carried  by 
the  lingual  incline  far  toward  the  central  line  of  the  tooth, 
much  so  as  to  be  in  marked  contrast  with  the  general 


so 


&" 


form  of  the  liogual  cusps  of  the  molars.  From  its  apex  a 
triangular  ridge  descends  to  join  that  from  the  mesio-buccal 
cusp  in  forming  the  transverse  ridge.  From  the  lingual  groove, 
the  lingual  marginal  ridge  rises  to  the  point  of  the  disto- 
lingual  cusp  (A)  and  then  falls  away  in  a  curve  to  form  the 
distal  marginal  ridge.  This  cusp  is  generally  rather  low,  but 
varies  much  in  these  teeth.  In  some  cases,  there  is  a  sharp 
triangular  ridge  descending  into  the  central  fossa,  but  more 
generally  this  ridge  is  slight. 

145.  The  distal  marginal  ridge  is  usually  made  to  ap- 
pear prominent  by  the  depth  of  the  principal  fossa.  It  is 
crossed  near  its  center  by  the  distal  groove. 

146.  The  principal  fossa  is  generally  deep  and  well 
rounded.  The  distal  triangular  ridges,  the  only  ones  descend- 
ing into  this  fossa,  are  generally  not  prominent,  but  occasion- 
ally they  are  sufficiently  so  to  render  the  fossa  very  angular. 
I  have  observed  many  in  which  the  enamel  in  this  fossa  was 
very  imperfect  and  the  bottom  of  the  fossa  broad  and  rough. 

147.  The  mesial  fossa  (z)  is  usually  sharp  and  deep  with 
smooth  sides  and  a  central  pit  that  is  frequently  the  seat  of 
caries. 

148.  The  buccal  surface  of  the  lower  first  deciduous 


LOWER    FIRST    DECIDUOUS    MOLAR.  IDS' 

molar  (Fig.  107)  is  remarkable  for  its  prominent  bucco-gin- 
gival  ridge  (a),  which  runs  from  the  mesio-buccal  to  the 
disto-buccal  angle,  and  stands  out  prominently  over  the  junc- 
tion of  the  crown  with  the  root.  From  mesial  to  distal ,  this 
ridge  slopes  toward  the  occluding  surface,  making  the  crown 
longer  at  the  mesial  angle  than  at  the  distal.  From  this 
ridge  the  surface  slopes  rapidly  toward  the  occluding  margin, 
and  more  rapidly  at  the  mesial  than  the  distal  portion.  From 
the  mesio-buccal  cusp  a  strong  ridge  of  enamel  runs  to  the 
more  prominent  portion  of  the  gingival  ridge  near  the  mesio- 
buccal  angle.  Otherwise  this  surface  is  nearly  flat.  The 
lingual  surface  is  usually  well  rounded,  but  is  broken  toward 
the  occluding  surface  by  the  prominence  of  the  mesio-lingual 
cusp,  and  the  sulcus  of  the  lingual  groove. 

149.  The  mesial  and  distal  surfaces  are  slightly  rounded. 
The  disto-buccal  and  lingual  angles  are  about  equal  in  promi- 
nence, but  the  mesio-buccal  and  lingual  angles  are  very  un- 
equal. The  mesial  surface  slopes  rapidly  to  the  lingual, 
makino;  the  linsfual  surface  much  shorter  than  the  buccal. 
The  mesio-buccal  angle  is  acute  and  prominent,  while  the 
mesio-lingual  is  very  obtuse  and  rounded. 

150.  The  root  of  this  molar  is  divided  into  two  prongs 
which  are  spread  widely  apart.  They  are  thin  from  mesial 
to  distal,  and  slightly  grooved ;  and,  from  buccal  to  lingual, 
broad.  They  taper  regularly  to  broad  flat  apexes,  which 
are  occasionally  bifurcated  near  their  apexes. 

151.  The  roots  of  the  deciduous  teeth  are  the  same  in 
number  and  general  characteristics  as  in  the  teeth  of  the 
same  denomination  in  the  permanent  set,  except  that  those 
of  the  molars  are  more  divergent.  This  spreading  of  the  roots 
accommodates  the  crowns  of  the  permanent  bicuspids,  which 
are  developed  between  the  roots  of  the  deciduous  molars. 
Those  of  the  lower  jaw  are  thin  from  mesial  to  distal,  broad 
from  labial  to  lingual,  and  grooved  along  their  flattened  sides. 
The  mesial  and  distal  roots  of  the  upper  deciduous  molars 


104  THE   PULP   CHAMBER. 

are,  also,  thin,  grooved,  and  widely  divergent.  The  lingual 
root  stands  boldly  to  the  lingual,  forming  a  wide  space  be- 
tween the  three,  for  the  crowns  of  the  upper  bicuspids.  In 
many  examples  the  lingual  and  distal  roots  are  joined  by 
broad  thin  connections  for  the  greater  part  of  their  length. 

THE    PULP    CHAMBER. 

152.  Every  tooth  has  a  cavity  in  the  center  of  the 
crown,  and  one  or  more  canals  extending  through  the  long 
axis  of  the  root,  or  roots,  to  the  apex.  This  cavity  contains 
a  tissue  composed  of  cellular  elements  imbedded  in  a  semi- 
gelatinous  matrix,  filling  every  part  of  the  space,  and  is 
richly  supplied  with  blood-vessels  and  nerves.  This  is  known 
as  the  pulp  of  the  tooth.* 

153.  The  central  cavity  in  the  tooth  is  usually  divided 
into  a  crown,  or  coronal  portion,  and  a  root  portion.  Its 
parts  are  familiarly  known  as  the  pulp  chamber  (crown 
cavity),  and  root  canal,  or  root  canals.  The  pulp  chamber  is 
comparatively  large,  and  the  root  canals  are  small,  tapering 
from  the  pulp  chamber  to  a  minute  opening  at  the  apex  of 
the  root,  known  as  the  apical  foramen.  In  those  teeth  that 
have  prominent  cusps,  as  the  bicuspids  and  molars,  there  is 
a  prolongation  of  the  pulp  toward  the  point  of  each  cusp. 
These  are  known  as  the  horns  of  the  pulp;  and  the  prolonga- 
tions of  the  chamber  are  designated  the  horns  of  the  pulp 
chamber. 

154.  The  size  of  the  pulp  chamber  and  of  the  root 
canals  varies  greatly  in  teeth  of  difierent  denominations;  and 
also  in  different  teeth  of  the  same  denomination.  In  the 
early  formative  stages  of  the  teeth,  it  is  very  large,  and 
diminishes  in  size  as  growth  proceeds,  until  the  tooth  is 
fully  formed.     Afterward  this  diminution  goes  on  slowly, 

*As  the  form  of  the  pulp  chamber  gives  the  exact  form  of  the  pulp,  no 
separate  description  of  the  pulp  will  be  given.  It  is  not  my  purpose  to  give 
any  histological  descriptions  in  this  work. 


THE   PULP   CHAMBER.  105 


until,  in  old  age,  it  is  often  nearly  obliterated.  In  the  forma- 
tive stage,  i.  e.,  during  the  growth  of  the  root  of  the  tooth, 
the  root  canal  is  large  and  funnel-shaped,  with  the  oj^en  end 
of  the  funnel  toward  the  apex  of  the  root.  As  growth  pro- 
ceeds, and  the  root  approaches  completion,  this  diminishes 
rapidly  till  the  root  is  fully  formed,  when  it  is  contracted  to 
a  small  foramen.  This,  however,  continues  to  diminish 
slowly.  Therefore,  the  size  of  the  pulp  chamber,  the  root 
canals,  and  the  apical  foramen,  are  greater  in  youth  than  in 
old  age.  However,  after  adult  age  is  reached,  the  diminu- 
tion in  size  is  usually  not  great.  During  this  time,  the  horns 
of  the  pulp  chamber  are  shortened  by  the  same  process  of 
formation  of  dentine  on  their  surface  that  is  going  on  in  all 
parts  of  the  pulp  chamber  and  root  canal.  Therefore,  the 
horns  of  the  j)ulp  become  shorter,  or  recede,  as  age  advances. 
Indeed,  the  whole  pulp,  very  slowly,  becomes  smaller. 

155.  Certain  processes,  when  present,  also,  serve  to  di- 
minish the  size  of  the  pulp  chamber  more  rapidly ;  especially 
abrasion  of  the  teeth,  a  matter  that  seems  to  depend  largely 
upon  the  character  of  the  occlusion.  When  the  occlusion  is 
such  that  there  is  much  rubbing,  or  sliding  motion,  of  the 
teeth  against  each  other,  wear  goes  on  rapidly.  This  seems 
to  induce  depositions  of  dentine  on  the  walls  of  the  pulp 
chamber,  which  reduces  its  size ;  and,  especially,  causes  the 
recession  of  the  horns  of  the  pulp.  In  this  way,  exposure  of 
the  pulp  from  the  wearing  away  of  the  dentine  is  delayed  or 
prevented.  In  many  instances  the  pulp  chamber  is  almost 
obliterated  in  the  molars  and  bicuspids,  and  recedes  root- 
wise  of  the  gingival  line  in  the  incisors  and  cuspids.  Slowly 
progressive  caries  or  erosion  of  the  teeth  often  induce  similar 
deposits. 

156.  In  the  incisors  and  cuspids,  the  pulp  chamber  and 
the  root  canal  are  not  sharply  differentiated.  The  latter  ta- 
pers, gradually,  from  the  full  size  of  the  largest  crown  por- 
tion to  a  small  foramen  at  the  apex  of  the  root.     In  teeth 


106  THE   PULP   CHAMBERS — UPPER  INCISORS. 

with  more  than  one  root,  the  transition  from  pulp  chamber 
to  root  canal  is  usually  sharply  defined,  the  former  being 
very  large  as  compared  with  the  pulpal  end  of  the  latter. 
Indeed,  the  general  form  of  the  pulp  is  a  diminished  counter- 
part of  the  form  of  the  surface  of  the  tooth,  except  that  it  is- 
in  every  way  more  slender, 

157.  Our  studies  thus  far  have  been  of  the  outer  surfaces 
of  the  teeth.  The  pulp  chambers  are  within,  and,  therefore, 
in  the  study  of  them,  dissections  must  be  made  to  expose 
them  to  view.  It  is  often  necessary  for  the  dentist  to  enter 
the  pulp  chamber  of  the  teeth  of  his  patients,  and  there  per- 
form delicate  operations  with  a  precision  which  demands  the- 
most  accurate  knowledge  of  this  cavity.  Therefore  this  work 
of  exposure,  and  examination,  of  the  pulp  chambers  of  teeth 
should  be  thorough,  as  a  preparation  for  operations  in  the 
mouth.  The  form  of  dissection  necessary  will  be  given  ia 
connection  with  the  teeth  as  they  are  individually  described. 

THE   PULP   CHAMBERS   OF    THE   UPPER    INCISORS. 

158.  The  pulp  chambers  and  root  canals  of  the  upper 
central,  and  lateral  incisors  are  so  similar,  the  description  of 
one  will  do  for  all. 

Dissection. — 1st.  Saw  the  tooth  through  on  the  gingi- 
val line,  at  the  labial  surface,  at  right  angles  with  the  long 
axis. 

2d,  Saw  the  tooth  from  labial  to  lingual,  along  the 
central  line  of  the  long  axis  from  end  to  end. 

3d.  Saw  the  tooth  from  mesial  to  distal,  along  the 
central  line  of  the  long  axis  from  end  to  end. 

159.  A  very  thin  saw  in  a  strong  frame  should  be 
used,  otherwise  the  lengthwise  dissections  should  be  made  to 
one  side  of  the  central  line  in  the  first  instance,  and  after- 
ward the  whole  length  of  the  pulp  chamber  exposed  by 
grinding  on  a  stone;  or  the  lengthwise  exposure  may  be 
made  by  catching  the  tooth  in  the  vise  and  removing  one- 


Fig.  108. 


Fig.  109. 


Fig.  110. 


Fig.  108*  (Par.  160).— The  Pulp  Chamber  of  the  Upper  Central  Incisor,  a,  b^ 
Mesio-distal  sections  of  the  young  teeth,  showing  the  three  short  horns  of  the  pulp  ; 
c,  mesio-distal  section  of  a  tooth  from  an  adult ;  d,  e,  labio-lingual  sections. 

Fig.  109*  (Par.  160).— Pulp  Chamber  of  the  Upper  Lateral  Incisor.— a,  6,  Mesio- 
distal  sections  ;  c,  labio-lingual  sections ;  d,  labio-lingual  section  of  a  very  long  lateral 
incisor. 

Fig.  110  *  (Par.  163)— Pulp  Chamber  of  the  Upper  Cuspids,  a,  b,  Mesio-distal  sections ; 
c,  d,  labio-lingual  sections. 


*  Illustration,  actual  size. 


THE   PULP   CHAMBERS — UPPER   INCISORS.  lOO" 

half  with  the  file,  or  by  grinding  on  an  emery  wheel.  After 
the  pulp  chamber  is  exposed  so  that  half  of  its  concavity 
remains  in  the  half  of  the  tooth,  and  has  been  ground 
smooth  and  flat,  it  should  be  inked  on  an  inked  pad  (such  as 
is  used  for  rubber  stamps  for  printing),  and  a  print  made 
from  it.  This  will  give  the  form  of  the  tooth  and  pulp 
chamber  in  silhouettes  similar  to  the  accompanying  illus- 
trations. The  printing  is  facilitated  by  sticking  the  tooth  to 
a  piece  of  hard  wax  for  convenience  in  handling.  Ordinary 
modeling  compound,  or  sealing  wax,  is  convenient  and  effec- 
tive. The  printing  is  usually  better  done  by  laying  ordinary 
writing  paper  on  a  sheet  of  semi-soft  rubber,  about  one-eighth 
inch  in  thickness.  This  is  specially  useful  when  the  ground 
surface  cannot  be  perfectly  flat,  as  in  curved  roots. 

160.  In  the  upper  central  and  lateral  incisors  (Figs.  108 
and  109),  there  is  no  distinct  division  of  the  pulp  cavity  into 
pulp  chamber  and  root  canal  ;  but  there  is  one  straight  canal, 
from  the  interior  of  the  body  of  the  crown  to  the  apex  of 
the  root,  of  which  the  crown  portion  is  the  larger.  In  young 
teeth,  this  has  very  distinctly  the  form  of  the  surface  of  the 
tooth  and  root,  except  that  it  is  much  more  slender.  The 
largest  diameter  of  the  cavity  is  about  level  with  the  gingi- 
val line  on  the  labial  surface.  From  this  point,  the  pulp 
chamber,  or  canal,  extends  toward  the  cutting  edge  of  the 
tooth,  about  two-thirds  the  length  of  the  crown,  sometimes 
■a  little  more,  often  less,  and  ends  in  a  thin  edge,  broad  from 
mesial  to  distal.  In  young  teeth  this  edge  has  three  short 
horns  (Fig.  108,  a,  6),  or  prolongations,  extending  toward  the 
three  small  cusps  seen  on  the  edge  of  unworn  incisors  (21). 

161.  From  the  gingival  line  toward  the  apex  of  the 
root  it  tapers  very  gradually  and  regularly  to  a  narrow  canal. 
Just  within  the  apex  of  the  root,  almost  at  the  end,  there  is 
usually  a  sudden  contraction  of  the  diameter  of  the  canal, 
lessening  it  from  one-third  to  one-half.  This  is  the  apical 
foramen ;  but  this  contraction  of  the  canal  is  not  usually 


110    THE   PULP   CHAMBERS — UPPER   CUSPID — LOWER   INCISORS. 

present  for  one  or  two  years,  or  more,  after  the  tooth  has 
taken  its  place  in  the  arch  [q.  v.,  154). 

162.  The  size  of  the  canal  becomes  smaller  from  youth 
to  old  age.  In  incisors  just  taking  their  places  in  the  arch, 
I  have  found  the  diameter  of  the  canal  at  the  gingival  line 
to  be  from  one-fourth  to  one-third  the  diameter  of  the  neck 
of  the  tooth.  In  early  adult  age,  the  canal  may  be  said  to 
average  about  a  fourth  the  diameter  of  the  neck  of  the  tooth, 
ranging  down  as  age  advances  to  one-iifth,  or  sixth,  and  even 
to  one-tenth.  In  the  lateral  incisor,  the  chamber  and  canal 
are  a  little  smaller  than  in  the  central,  but  larger  in  propor- 
tion to  the  size  of  the  tooth. 

THE   UPPER   CUSPID. 

163.  The  pulp  chamber  and  root  canal  of  the  upper 
cuspid  (Fig.  110)  is  about  the  same  in  form  as  that  of  the 
central  and  lateral  incisors,  except  that  the  coronal  extremity 
has  the  central  horn  much  extended  toward  the  apex  of  the 
cusp  of  the  tooth,  and  the  lateral  horns  are  practically  absent. 
The  canal  is  proportionally  somcM^hat  smaller.  However, 
this  tooth  is  often  somewhat  flattened  at  the  neck,  the  long 
diameter  being  from  labial  to  lingual.  In  this  case  the  pulp 
canal  at  the  neck,  and  from  thence  toward  the  apex  of  the 
root,  is  also  much  flattened  in  the  same  direction,  but  is  pro- 
gressively rounded  as  the  apex  is  approached.  In  some 
examples,  the  labio-lingual  diameter  of  the  canal  is  double 
the  mesio-distal.  As  age  advances,  and  the  canal  becomes 
smaller,  the  opening  is  occasionally  reduced  to  a  mere  slit. 

PULP   CHAMBER    OF    THE    LOWER   INCISORS. 

164.  (Fig.  111).  The  coronal  portion  of  the  pulp 
chamber  of  the  lower  incisors  is  much  flattened.  At  the 
level  of  the  gingival  line,  the  long  diameter  is  from  labial  to 
lingual.  The  chamber  extends  toward  the  cutting  edge  of 
the  tooth,  about  two-thirds  the  length  of  the  crown,  and  in 


6H?(ft 


d 
Fig.  111. 


Fig.  112. 


Fig.  Ill  *  (Par.  164).— Pulp  Chambee  op  the  Lower  Central  and  Lateral  Incisors. 
■a,  b,  c,  Labio-lingual  sections,  showing  differences  of  form  of  the  pulp  chamber ;  d,  mesio- 
distal  section ;  e,  f,  laMo-lingual  sections,  showing  the  more  usual  forms  of  the  pulp 
chamber  ;  g,  mesio-distal  section,  showing  large  pulp  chamber. 

Fig.  112*  (Par.  165).— Pulp  Chamber  of  the  Lower  Cuspids,  a,  Labio-Ungual  section, 
showing  a  small  pulp  chamber ;  b,  labio-lingual  section,  showing  a  verj'  large  pulp 
chamber ;  c,  mesio-distal  section. 


Illustration,  actual  size. 


THE   PULP   CHAMBER — LOWER   CUSPID.  113 

this  extension  its  diameter  is  progressively  diminished  from 
labial  to  lingual,  and  extended  from  mesial  to  distal,  follow- 
ing the  contour  of  the  surface  of  the  tooth,  and  ends  in  a 
thin  edge.  In  young  teeth  this  has  three  short  projections 
toward  the  slight  cusps  seen  on  the  cutting  edges  of  the 
young,  unworn  teeth.  The  root  has  usually  a  narrow  slit- 
like opening  for  the  greater  portion  of  its  length  {d^  g),  cor- 
responding with  the  form  of  the  flattened  roots.  In  many 
instances,  however,  the  root  canal  is  divided  into  two  por- 
tions, or  canals,  for  a  part  of  its  length  {e,f).  In  the  adult, 
these  canals  are  usually  very  small,  the  point  of  separation 
into  two  canals  being  irregular,  but  usually  slightly  root-wise 
from  the  level  of  the  gingival  line.  It  may  occur  at  about 
the  level  of  the  gingival  line,  or  the  canal  may  remain  single 
for  half  the  length  of  the  root,  and  then  be  divided  for  a 
space,  the  two  uniting  again  before  reaching  the  apex.  Gen- 
erall}^,  there  is  but  one  apical  foramen.  Instances  occur  in 
which  there  are  two,  each  canal  remaining  distinct  to  the 
end.  As  age  advances,  the  canals  of  the  lower  incisors  often 
become  very  minute. 

PULP   CHAMBER   OF   THE    LOWER   CUSPID. 

165.  The  pulp  chamber,  and  the  root  canal  of  the  lower 
cuspid  (Fig.  112)  are  variable  in  size  and  form.  At  the  neck 
of  the  tooth  the  chamber  is  usually  irregularly  flattened, 
with  the  longer  diameter  from  labial  to  lingual,  and  the 
labial  portion  wider  than  the  lingual.  The  coronal  portion 
extends  about  two-thirds  of  the  length  of  the  crown  toward 
the  point  of  the  cusp,  ending  in  a  point,  or  horn,  which  is 
often  very  slender.  The  form  of  the  root  portion  of  the 
canal  depends  on  the  form  of  the  root.  It  is  sometimes 
nearly  round,  but  more  frequently  it  is  sharply  flattened  for 
the  greater  portion  of  its  length,  becoming  more  rounded 
toward  the  apex.  Occasionally,  this  canal  is  divided  for  a 
part  of  the  length  of  the  root.      Also,  the  root  is  sometimes 


114    THE    PULP    CHAMBER BICUSPIDS UPPER    FIRST    BICUSPID. 

■divided,  a  very  small  prong  appearing  on  its  lingual  side. 
In  this  there  is  usually  a  very  small  canal  that  is  difficult  to 
enter  with  a  broach.  In  some  lower  cuspids  the  canal  is  very 
■small  (a),  in  others,  very  large  (b).  In  a  few  instances  I  have 
seen  it  more  than  one-third  the  diameter  of  the  root  in  the 
adult.  In  this  case  the  diameter  of  the  canal  is  greater  than 
the  thickness  of  the  walls  of  dentine  and  cementum  by  which 
it  is  inclosed.  This  renders  the  pulp  very  liable  to  exposure 
in  excavating  carious  cavities. 

PULP    CHAMBERS    OF    THE    BICUSPIDS. 

166.  Dissections. — 1st.  Divide  the  crown  from  the  root 
on  the  gingival  line  with  a  fine  saw. 

2d.  Divide  the  tooth  from  labial  to  lingual  through  its 
length  with  a  fine  saw ;  or  remove  the  distal  half  of  the 
tooth  with  the  file,  or  stone.  These  two  dissections  will  usu- 
ally exhibit  the  pulp  chamber  and  root  canals  sufficiently, 
though  in  the  single-rooted  teeth  with  two  canals  it  is  better 
to  divide  the  root  crosswise  at  the  middle  of  its  length,  or  at 
several  points. 

PULP   CHAMBER   OF   THE   UPPER   FIRST    BICUSPID. 

167.  The  pulp  chamber  and  root  canals  of  this  tooth 
differ  from  those  of  the  incisors  and  cuspids,  by  having  the 
coronal  chamber  distinguished  sharply  from  the  root  canals 
(Fig.  113,  <i,  e).  The  chamber  is  centrally  located  in  the  long 
axis  of  the  crown  of  the  tooth,  the  lateral  walls  being  about 
equal  in  thickness.  The  center  of  the  ]:)ulp  chamber  is  about 
level  with  the  gingival  line,  or  a  little  toward  the  occluding 
surface.  The  occluding  walls  are  thicker  than  the  lateral, 
and  vary  in  thickness  from  about  one-third  to  two-thirds  of 
the  length  of  the  crown  of  the  tooth.  The  form  of  the  pulp 
corresponds  closely  with  the  form  of  the  tooth.  A  horn 
extends  from  the  coronal  portion  toward  the  apex  of  each 
<;usp.    The  buccal  horn  rises  from  the  extreme  buccal  part  of 


Fig.  115. 


Fig.  116. 


Fig.  113  *  (Par.  167).— Pulp  Chamber  and  Root  Canals  of  the  Upper  First  Bicuspids 
b,  Labio-lingual  section  of  single-rooted  tooth,  with  single  canal  divided  near  the  apes 
of  the  root ;  a,  cross-section  of  the  same ;  d,  labio-lingual  section  of  a  single-rooted  tooth 
with  two  canals,  which  connect  at  one  point ;  c,  cross-section  of  the  same,  a  little  root- 
wise  from  the  pulp  chamber ;  e,  labio-lingual  section  of  a  double-rooted  tooth,  showing 
the  more  usual  form  of  the  chambers  and  canals. 

Fig.  114*  (Par.  168).— Pulp  Chamber  and  Root  Canals  of  the  Upper  Second  Bi- 
cuspid, o,  Labio-lingual  section  showing  chamber  with  a  long  slender  horn,  also  two 
canals  which  unite  in  the  apical  third  of  the  root ;  6,  cross  section  of  a  root  with  two 
canals ;  c,  cross  section  of  a  root  with  a  single  large  canal ;  d,  labio-lingual  section  of  a 
single  root  with  two  canals  ;  e,  f,  labio-lingual  sections  shoAving  the  more  usual  form  of 
the  pulp  chamber  and  root  canal  of  the  tooth. 

Fig.  115  *  (Par.  169).— Pulp  Chamber  and  Root  Canals  of  the  Lower  First  Bicuspid. 
a,  Labio-lingual  section  showing  the  more  usual  form ;  b,  labio-lingual  section  showing 
a  peculiar  and  very  unusual  division  of  the  root  canal ;  c,  cross  section  in  the  body  of  the 
root. 

Fig.  116*  (Par.  169).— Pulp  Chamber  and  Root  Canal  of  the  Lower  Second  Bi- 
cuspid, a,  b,  Labio-lingual  sections  showing  the  more  usual  forms  of  the  chamber  and 
eanal  in  this  tooth. 


*  Illustration,  actual  size. 


THE   PULP   CHAMBER — UPPBE   SECOND   BICUSPID.  117 

the  pulp,  while  the  lingual  horn  rises  from  the  extreme  lin- 
gual portion.  Sometimes,  especially  in  long  cusped  teeth, 
they  are  very  long  and  slender,  extending  far  toward  the 
points  of  the  cusps,  and  in  rare  cases  almost,  or  even  quite  to 
the  enamel.  As  age  advances,  they  become  shorter,  and  in 
old  age  have  almost  disappeared.  In  thick-necked  teeth 
with  short  cusps,  the  horns  of  the  pulp  chamber  are  short, 
and  the  occluding  wall  is  usually  very  thick. 

167.  The  root  canals  in  bicuspids  that  have  two  roots 
pass  from  the  pulp  chamber  through  the  center  of  each  root 
to  its  apex,  and  are  known  as  the  buccal  and  lingual  root 
canals  {e).  The  buccal  canal  arises  from  the  ejitreme  buccal 
side  of  the  pulp  chamber,  and  the  lingual  canal  from  the 
extreme  lingual  side,  and  their  course  is  almost  parallel  with 
the  walls  of  these  two  portions  of  the  pulp  chamber.  The 
floor  of  the  chamber  is  rounded  over  in  an  arch  from  one 
canal  to  the  other.  Each  canal  begins  in  a  funnel-shaped 
opening,  which  leads  into  a  narrow  round  canal,  which 
tapers  gradually  to  the  apical  foramen.  Many  of  the  upper 
first  bicuspids  have  only  one  root ;  but  they  generally  have 
two  root  canals  almost  exactly  similar  to  those  with  two 
roots.  Occasionally,  however,  these  come  together  and  end 
in  one  apical  foramen,  or  there  may  be  a  communication 
between  the  two  canals  in  some  part  of  their  course  {d).  More 
rarely,  the  upper  first  bicuspid  has  one  broad  (from  buccal  to 
lingual)  flat  canal  passing  through  the  whole  length  of  its 
single  root.     Sometimes  this  is  divided  near  the  apex  {b). 

PULP    CHAMBER    OF    THE    UPPER    SECOND    BICUSPID. 

168.  The  pulp  chamber  of  the  upper  second  bicuspid 
(Fig.  114)  is  very  similar  to  that  of  the  first  {q.  ■?;.,  167) ;  but 
the  horns  of  the  pulp  are  usually  shorter.  In  this  tooth  there 
IS  generally  but  a  single  root  canal  (e,  /).  This  is  approached 
by  an  opening  that  is  broad  from  buccal  to  lingual,  and 
tapers  gradually  toward  the  apex  of  the  root,  ending  in  a 


118  THE    PULP   CHAMBERS — LOWER    BICUSPIDS. 

narrow  apical  foramen.  The  canal  is  often  quite  large,  and 
the  demarkation  of  the  pulp  chamber,  as  distinguished  from 
the  root  canal,  very  indistinct,  or  entirely  absent.  Examples 
are  not  infrequent,  however,  in  which  there  are  two  root 
canals  in  the  single  root  [d).  They  are  then  similar  to  those 
of  the  first  bicuspid  ;  but,  sometimes,  the  two  canals  end  in 
a  common  apical  foramen  [a). 

PULP    CHAMBERS   OF   THE    LOWER    BICUSPIDS. 

169.  The  pulp  chambers  of  the  lower  bicuspids  (Figs. 
115  and  116)  seldom  show  a  marked  distinction  from  the  root 
canals.  There  is,  however,  usually  a  coronal  bulbus  portion 
which  connects  with  the  pulp  canal  proper  by  an  extended 
funnel-shaped  constriction  (a,  b).  In  the  lower  first  bicuspid, 
the  coronal  extremity  ends  in  a  horn,  which  extends  toward 
the  point  of  the  buccal  cusjd.  This  horn  may  be  short  and 
obtuse,  or  long  and  pointed.  There  is,  generally,  a  well 
marked  protrusion  toward  the  lingual  cusp,  but  no  extended 
horn.  It  is  rather  an  enlargement  of  the  l)ulb  in  that  direc- 
tion. In  the  lower  second  bicuspid,  this  protrusion  is  more 
considerable,  and  in  some  examples  it  is  elongated  into  a 
slender  point,  especially  in  young  teeth  (Fig.  116,  h).  In  the 
three  cuspids,  lower  second  bicuspids  (162,  Fig.  49)  there  are 
two  of  these  on  the  lingual  side,  spreading  toward  the  mesial 
and  distal.  They  are  generally  short,  but  by  their  protrusion 
are  brought  rather  nearer  the  surface  of  the  tooth  than  other 
horns  of  the  pulp  ;  and  are,  therefore,  more  liable  to  be 
opened  into  when  excavating  proximate  cavities. 

170.  The  root  canals  of  the  lower  bicuspids  are  usually 
large  in  the  first  half,  tapering  to  a  fine  canal  in  the  apical 
third,  of  their  length.  The  canal  of  the  lower  first  bicuspid 
is  usually  nearly  round,  and  the  second  is  considerably  flat- 
tened ;  and  in  both  they  are  usually  straight.  Bifurcations 
of  these  canals  are  rare,  but  occur  occasionally.  In  the  illus- 
trations (Fig.  115,  b)  one  is  shown  dividing  in  such  a  way 


THE    PULP    CHAMBERS UPPER   MOLARS.  119 

that  the  division  would  not  be  likely  to  be  detected  by  a 
broach. 

PULP    CHAMBERS    OF    THE    UPPER    MOLARS. 

171.  Dissections. — 1st.  With  a  fine  saw,  separate  the 
crown  from  the  root  level  with  the  gingival  line. 

2d.  Cat  away  the  mesial  surface  of  the  crown  and  the 
mesial  surface  of  the  mesial  and  lingual  roots,  with  the  file 
or  a  corundum  stone,  till  the  canals  in  each  are  fully  ex- 
posed. As  the  mesial  root  is  generally  curved,  some  care  is 
required  to  fully  expose  the  full  length  of  the  canal  without 
cutting  too  far  in  the  central  portion  of  its  length.  If  the 
curved  surface  is  made  smooth,  good  prints  can  generally  be 
made  by  using  a  piece  of  semi-soft  rubber  under  the  paper, 
and,  while  pressing  it  to  the  paper,  rolling  the  tooth  so  as  to 
bring  all  of  the  length  of  the  curved  surface  in  contact. 

3d.  Cut  away  the  buccal  surface  so  as  to  expose  the 
pulp  chamber  and  canals  of  the  two  buccal  roots,  observing 
the  same  precautions  as  in  the  second  dissection. 

In  the  first  dissection,  both  crown  and  root  should  be 
examined.  First,  clean  the  portion  of  the  chamber  in  the 
crown  to  study  carefully  its  horns  and  its  general  shape  or 
contour  with  relation  to  the  outer  surface  of  the  tooth.  The 
root  canals  should  be  cleaned  with  the  broach,  and  their  size 
and  direction  carefully  studied ;  also,  the  position  of  the 
openings  leading  from  the  pulp  chamber  should  be  studied 
with  regard  to  their  relation  to  the  several  points  of  the  sur- 
face of  the  crown.  This  latter  is  especially  important. 
Several  dissections  should  be  made  of  each  of  the  upper 
molars. 

4th.  Grind  away  the  root  portion  of  the  first  dissection, 
printing  occasionally  till  the  bifurcation  of  the  roots  is 
reached. 

172.  The  pulp  chamber  of  the  upper  molars  is  very 
distinct  from  the  pulp  canals ;  the  latter  often  leaving  the. 


120  THE    PULP    CHAMBERS UPPER    MOLARS. 

former  hy  very  small  openings  (Fig.  117).  The  average 
diameter  of  the  pulp  chamber  is  about  equal  to  the  thickness 
of  the  lateral  walls  by  which  it  is  surrounded,  sometimes 
more,  sometimes  less.  The  occluding  wall  is  usually  con- 
siderably thicker.  The  form  of  the  pulp  chamber  is  generally 
similar  to  that  of  the  crown  of  the  tooth ;  but  the  horns  in 
the  young  tooth  are  often  quite  slender  as  compared  with 
the  cusps,  and  penetrate  far  toward  the  enamel.  The  length 
of  these  diminish  as  age  advances.  In  teeth  much  flattened 
from  mesial  to  distal,  as  often  occurs  in  the  upper  first 
molars,  and  especially  with  the  second,  the  equal  thickness 
of  the  lateral  walls  is  usually  maintained  pretty  closely,  so 
that  the  flattening  of  the  pulp  chamber  seems  out  of  propor- 
tion to  the  form  of  the  tooth. 

173.  The  floor  of  the  pul]3  chamber  is  rounded  or  arched 
in  the  center,  and  falls  away  toward  the  mouths  of  the  canals. 
The  latter  are  situated  in  the  position  of  the  angles  of  a  tri- 
angle {the  molar  triangle)  (Figs.  118  and  119),  the  mesial  line 
of  which  is  the  longest,  the  buccal  the  shortest,  and  the  distal 
the  intermediate  length.  For  the  first  molar,  this  triangle  is 
%vell  shown  in  the  illustrations  representing  sections  a  little 
rootwise  from  the  floor  of  the  pulp  chamber  (c).  This  is 
best  seen  in  the  specimen  itself;  and  the  position  and  the  di- 
rection of  the  canals,  with  relation  to  the  walls  of  the  pulp 
chamber  and  the  main  points  of  the  surface  of  the  crown, 
should  be  carefully  studied. 

174.  The  opening  into  the  lingual  root  (Fig  117,  d)  is 
the  simplest  and  most  direct.  Generally,  it  begins  in  a  funnel- 
shaped  opening  inclining  to  the  lingual,  which  quickly 
narrows  to  the  dimensions  of  a  moderately  small  canal,  and 
continues  to  taper  to  the  apical  foramen.  It  is  usually 
straight,  or  but  slightly  curved. 

175.  The  opening  of  the  mesial  canal  is  under  the 
mesio-buccal  cusp,  close  against  the  mesio-buccal  angle  of 
the  pulp  chamber.    It  often  happens  that  this  canal  oj)ens  in 


fifcr 


Fig.  117. 


D&OOOd 


Fig.  118. 


Fig.  119. 


Fig.  120. 


Fig.  121. 


Fig.  117*  (Par.  172).— Pulp  Chamber  and  Root  Canals  of  the  Upper  First  Molar. 
a,  Labio-lingual  section  showing  the  chamber  and  the  canals  in  the  distal  and  lingual 
roots ;  b,  d,  mesio-distal  sections  showing  the  pulp  chamber  and  the  canals  in  the  mesial 
and  distal  roots ;  c,  labio-lingual  section  showing  the  pulp  chamber  and  the  canals  in 
the  mesial  and  lingual  roots. 

Figs.  118,*  119*  (Par.  173).— Pulp  Chamber  and  Root  Canals  of  the  Upper  First 
Molars,  cross  sections,  a,  Centrally  through  the  pulp  chamber ;  6,  section  just  at  the 
floor  of  the  pulp  chamber ;  c,  section  a  little  rootwise  from  the  pulp  chamber,  showing 
the  canals,  and  the  form  of  the  molar  triangle. 

'  Fig.  120  *  (Par.  177).— Pulp  Chamber  and  Root  Canals  of  the  Upper  Second  Molar. 
o,  Mesio-distal  section  showing  pulp  chamber  and  the  canals  in  the  mesial  and  distal 
roots ;  b,  labio-lingual  section  showing  the  chamber  and  the  canals  in  the  distal  and 
lingual  roots. 

Fig.  121  *  (Par.  178).— Pulp  Chamber  and  Root  Canals  in  the  Upper  Third  Molar. 
a,  Labio-lingual  section  showing  pulp  chamber  and  the  canals  in  the  mesial  and  lingual 
roots ;  5,  mesio-distal  section  of  the  single  rooted  tooth  showing  the  fonn  of  the  pulp 
•chamber  and  the  mesial  and  distal  root  canals. 


*  Illustration,  actual  size. 


THE    PULP    CHAMBERS UPPER    MOLARS.  123 

a  groove  in  the  angle  of  the  chamber  (Fig.  119,  6),  making 
this  the  thinnest  point  in  the  dentinal  walls  surrounding  it. 
In  young  teeth,  the  mouth  of  the  canal  is  of  a  flattened 
funnel-shape,  which  is  quickly  contracted  into  a  very  fine 
canal ;  but  in  the  adult,  it  often  begins  as  a  fine  canal.  Its 
course  at  first  is  to  the  buccal  and  mesial,  and  then  curves  to 
the  distal.  It  is  usually  distinctly  flattened,  and  often  has 
a  thin  edge  to  the  lingual.  It  is  often  a  very  difiicult  canal 
to  clean  with  a  broach.  To  find  this  canal  the  point  of  the 
broach  should  be  directed  into  the  mesio-buccal  angle  of 
the  pulp  chamber;  and,  while  held  against  the  wall  within 
this  angle,  it  is  slid  toward  the  root.  It  will  rarely  fail  to 
glide  into  the  canal. 

176.  The  distal  canal  usually  begins  abruptly  as  a  fine 
opening  (Fig.  117,  «,  c),  situated  at  the  disto-buccal  angle  of 
the  floor  of  the  pulp  chamber  (Figs.  118  and  119) ;  so  that  a 
broach  pressed  into  that  angle  will  easily  glide  into  it.  But 
in  some  instances,  especially  in  the  upper  second  molars,  the 
opening  is  in  the  floor  of  the  pulp  chamber  at  a  little  distance 
from  the  immediate  angle  toward  the  center  of  the  floor,  and 
then,  in  positions  which  limit  the  use  of  the  eye,  it  is  often 
diflacult  to  find.  In  teeth  much  flattened  at  the  neck,  the 
opening  of  this  canal  may  begin  very  close  to  the  mouth  of 
the  mesial  canal  (Fig.  120,  a),  or  close  against  the  distal  wall 
of  the  chamber,  half  way  from  the  buccal  to  the  lingual 
wall,  or,  anywhere  between  this  point  and  the  disto-buccal 
angle.  The  first  direction  of  the  canal  will  vary  according 
to  its  position.  If  it  is  found  in  a  fairly  well-defined  disto- 
buccal  angle  of  the  chamber,  its  direction  will  be  a  little 
inclined  to  the  distal,  and  the  broach  will  penetrate  it  easily ; 
if  in  the  floor  of  the  chamber,  it  will  sometimes  be  straight, 
as  in  the  former  case  ;  but  more  generally  the  first  direction 
will  be  to  the  distal  and  buccal,  with  considerable  curve 
afterward.  If  found  close  to  the  mesial  canal,  its  course  is 
usually  first  sharply  to  the  distal,  when  it  curves  rather 


124  THE    PULP    CHAMBERS — ^LOWER    MOLARS. 

abruptly  toward  the  apex  of  root.  If  found  along  a  smooth 
or  curved  distal  wall,  the  course  will  generally  be  to  the 
distal  and  buccal,  with  but  little  curve.  This  canal  is  usually 
very  fine  from  its  beginning,  and  almost,  or  quite  round. 

177.  While  the  canals  are  similar  in  all  of  the  upper 
molars,  there  are  differences  in  the  form  of  the  floor  of  the 
pulp  chamber  that  may  be  briefly  generalized.  The  pulp 
chamber  of  the  upper  second  molar  (Fig.  120)  is  usually  much 
more  flattened  from  mesial  to  distal  than  in  the  first  molar. 
This  changes  the  relation  of  the  mouths  of  the  canals  some- 
what, rendering  the  distal  angle  of  the  triangle  formed  by 
them  more  obtuse,  and  brings  the  mouth  of  the  distal  canal 
nearer  the  mesial  line  of  the  triangle,  so  that  it  seems  to  be 
found  along  the  distal  wall  of  the  narrowed  chamber.  In 
others,  it  is  found  in  the  extreme  buccal  portion  crowded 
close  against  the  mouth  of  the  mesial  canal. 

178.  The  position  of  the  openings  of  the  canals  in  the 
upper  third  molar  (Fig.  121)  is  usually  much  the  same  as  in 
the  first  and  second,  varying  so  as  to  resemble  either.  Occa- 
sionally there  is  more  than  the  usual  number;  and  others 
with  only  one  or  two.  When  there  is  but  one,  it  is  com- 
monly quite  large.  Four,  five,  or  even  seven,  or  eight,  are 
sometimes  found. 

PULP   CHAMBERS    OF    THE   LOWER   MOLARS. 

179.  Dissections.  1st.  Saw  the  tooth  through  the  gin- 
gival line  dividing  the  crown  from  the  root.  This  cut  will 
pass  through  the  body  of  the  pulp  chamber  and  give  a  good 
view  of  the  roof,  and  floor,  and  a  good  idea  of  the  general 
form.  The  root  canals  should  be  cleaned  and  examined  with 
the  broach. 

2d.  Saw  the  tooth  through  from  end  to  end  centrally 
from  mesial  to  distal,  or  grind  or  file  away  the  buccal  side 
till  the  pulp  chamber  and  the  root  canals  are  exposed.  As 
there  are  usually  two  canals  in  the  mesial  root,  an  exact 


o  m9B 

Q  on  99 


g  h 

Pig.  123. 


BV 


9 


Fia:.  124. 


ff^^ 


Fig.  125. 

Fig.  122  *  (Par.  180).— Pulp  Chamber  and  Root  Canals  of  the  Lower  First  Molar. 
a,  h,  Mesio-distal  sections  showing  the  form  of  the  pulp  chamber  and  root  canals ;  c, 
bucco-lingual  section  showing  the  canals  in  the  mesial  root. 

Fig.  123*  (Par.  180).— Cross-Sections  Through  the  Crown  and  Root  op  the  Upper 
First  Molar,  showing  the  pulp  chamber  and  the  root  canals,  d,  g,  Sections  through  the 
pulp  chamber ;  e,  h,  sections  a  little  rootwise  from  the  pulp  chamber ;  /,  i,  sections  near 
ai)ex  of  root. 

Fig.  124*  (Par.  180).— Pulp  Ch.amber  and  Root  Canals  of  the  Lower  Second  Molar. 
a,  c,  Mesio-distal  sections,  showing  the  fonn  of  the  pulp  chamber  and  root  canals ;  b, 
bucco-lingual  section  of  the  distal  root  and  crown  ;  d,  bucco-lingual  section  through  the 
mesial  root  and  crown,  showing  two  canals  with  communication  in  the  apical  third  of 
the  root.    This  communication  is  not  very  common. 

Fig.  125*  (Par.  182).— Pulp  Chamber  and  Root  Canals  of  the  Upper  Third  Molar. 
o,  c,  In  double-rooted  teeth ;  b,  single-rooted  teeth. 

*  Illustration,  actual  size. 


THE   PULP   CHAMBERS — LOWER   MOLARS.  127 

central  cut  from  mesial  to  distal  will  generally  fail  to  expose 
the  canals,  and  the  cut  will  be  better  made  at  a  slight  angle, 
so  as  to  expose  either  the  labial  or  lingual  canal  of  the  mesial 
root. 

3d.  G-rind,  or  file,  away  the  mesial  surface  of  the  crown 
and  root  till  the  pulp  chamber  and  the  whole  length  of  the 
canals  in  the  mesial  root  are  exposed.  As  this  root  is  usually 
curved,  the  cutting  must  be  done  with  care,  and  the  curve 
followed. 

4th.  Cross  sections  of  the  roots  should  be  made  at 
intervals.  An  excellent  study  is  to  begin  grinding  at  the 
apex  of  the  roots,  printing  occasionally,  and  continuing  the 
grinding  until  the  pulp  chamber  is  reached.  This  will  display 
cross  sections,  at  intervals,  of  the  entire  root  canals.  Enough 
of  these  dissections  should  be  made,  of  each  of  the  lower 
molars,  to  make  the  student  familiar  with  each  class. 

180.  The  pulp  chamber  of  the  lower  molars  (Figs.  122, 
123,  124)  has  the  same  general  form  as  the  surface  of  the 
crown,  but  is  generally  rather  more  angular.  The  wall  of 
the  chamber  toward  the  occluding  surface  is  convex  toward 
the  pulp ;  the  horns  extend  from  the  extreme  angles  toward 
the  apex  of  each  cusp.  The  floor,  through  the  central  23or- 
tion,  is  arched  or  convex  from  mesial  to  distal,  and  concave 
from  buccal  to  lingual.  The  mesial  wall  of  the  cavity  is 
flat,  and  longer  than  the  distal.  The  mesio-buccal  and  mesio- 
lingual  angles  are  sharp  and  projecting,  while  the  distal 
angles  are  rounded  (Fig.  123,  d,  g).  The  size  of  the  chamber 
varies  much.  In  youth,  its  diameter  is  often  as  much  as 
two-fifths  of  the  crown,  and  seldom  less  than  one-third.  This 
diminishes  as  age  advances,  and  in  old  age,  it  is  often  very 
small,  or  especially  where  there  has  been  considerable  abra- 
sion of  the  teeth,  the  pulp  chamber  may  be  almost  obliterated. 

181.  The  root  canals  of  the  lower  molars  proceed  from 
the  mesial  and  distal  portions  of  the  pulp  chamber  (Fig.  122, 
«,  b).     The  mesial  canal,  at  its  mouth,  is  usually  about  as 


128  THE   PULP   CHAMBERS — LOWER   MOLARS. 

broad  from  buccal  to  lingual  as  the  whole  breadth  of  the 
chamber,  includmg  its  angular  projections.  Either  at,  or  a 
little  root  wise  from  the  floor  of  the  pulp  chamber,  it  is  usu- 
ally divided  into  two  very  small  canals  which  diverge  at 
first,  and  approach  each  other  afterward,  but  usually  remain 
distinct,  each  ending  in  its  own  apical  foramen  (Fig.  122,  c). 
Occasionally,  however,  they  are  united  in  the  apical  third  of 
the  root,  and  end  in  a  common  apical  foramen.  Again,  there 
may  be  a  communication  between  them  in  the  apical  portion 
of  the  root,  each  canal  remaining  otherwise  complete  in  itself. 
A  few,  have  one  broad  flattened  canal  (Fig.  123,  d,  e,/). 
These  canals  are  usually  minute,  and  very  diflicult  to  thor- 
oughly clean  with  the  broach,  though  the  mesio-buccal  canal 
is  usually  easily  found,  if  the  pulp  chamber  is  thoroughly 
opened.  By  placing  the  point  of  the  broach  in  the  mesio- 
buccal  angle  of  the  chamber  and  pushing  it  gently  on,  it 
will  generally  glide  into  the  canal.  The  first  direction 
inclines  to  the  mesial  and  buccal,  after  which  it  curves  to 
the  distal  and  lingual  (Fig.  122,  c).  Generally,  these  curves 
are  easy,  without  short  bends.  The  broach  easily  glides 
into  the  mesio-lingual  canal  by  placing  the  point  in  the 
mesio-lingual  angle  of  the  pulp  chamber  and  sliding  it 
towarfl  the  root.  The  first  inclination  is  to  the  mesial,  but 
occasionally  to  the  lingual,  after  which  it  curves  to  the  distal 
and  buccal. 

182.  The  distal  canal  is  approached  by  a  funnel-shaped 
opening,  of  which  the  central  part  of  the  distal  wall  of  the 
pulp  chamber  becomes  a  portion.  Its  direction  is  a  little  to 
the  distal,  and  is  generally  very  nearly  straight  to  the  apex. 
At  first,  it  is  flattened,  with  the  long  diameter  from  buccal 
to  lingual,  and  progressively  becomes  rounded,  and  tapers 
regularly  to  the  apical  foramen.  It  is  generally  much  larger 
than  the  canals  of  the  mesial  root  and  is  easily  cleaned  with 
the  broach.  If  the  mouth  is  wide  open,  and  the  handle  of 
the  broach  brought  against  the  upper  central  incisors  with 


VARIATIONS   OF    THE   FORM    OF   PULP   CHAMBERS.  1'29 

the  point  directed  against  the  posterior  wall  of  the  pulp 
chamber,  it  will  easily  glide  into  the  canal,  and  pass  to  the 
apical  foramen.  This  particular  position  for  easily  entering 
the  distal  canal  is  important,  for  all  the  lower  molars.  Occa- 
sionally, the  lower  third  molar  has  but  one  root  canal  (Fig. 
125 ,  6)  and  is  then  generally  very  large.  More  rarely,  only  a  sin- 
gle canal  will  be  found  in  the  lower  second  molar,  but  gener- 
ally, the  canals  of  the  second  and  third  lower  molars  are 
similar  to  those  of  the  first.  The  pulp  chambers  are  usually 
smaller,  and  oftener  irregular  in  outline.  The  lower  third 
molar  has,  occasionally,  a  very  large  pulp  chamber. 

VARIATIONS    OF    THE    FORM    OF    PULP    CHAMBERS. 

183.  Many  variations  of  form  occur  in  the  pulp  cham- 
bers and  root  canals.  The  roots  of  the  teeth  may  be  abnor- 
mally crooked  ;  and  then  the  canals  will  be  abnormally 
crooked.  In  many  instances,  the  pulp  chamber  will  have  in 
it  secondary  formations,  called  nodules,  which  may  be  adher- 
ent to  the  walls,  or  block  the  mouths  of  the  canals  and  pre- 
vent a  broach  gliding  into  them.  These  also  occur 
occasionally,  within  the  canals,  partially  blocking  the  way 
of  the  broach.  Sometimes  the  pulp  chamber  will  be  filled 
with  nodular  deposits  so  completely  that  there  seems  to  be 
no  room  for  the  tissues  of  the  pulp.  These  deposits  will 
have  to  be  removed  before  the  root  canals  can  be  reached 
and  entered,  after  which  the  canals  will  generally  be  found 
open.  These  deposits  occur  within  the  pulp  chambers  of  any 
of  the  teeth ;  but  they  cause  annoj^ance  more  frequently  in 
the  molars. 

184.  Occasionally  lateral  openings  occur  from  the  root 
canals  to  the  surface  of  the  root.  I  have  seen  more  of  these 
from  the  canals  of  the  lower  molars  than  any  other  teeth. 
Generally  they  follow  the  course  of  the  dental  tubules,  and 
open  on  the  side  of  the  root.  They  may  diverge  to  one  side 
and  curve  toward  the  apex  of  the  root.     These  cannot  often 


130  PULP    CHAMBERS    OF    THE    DECIDUOUS    TEETH. 

be  detected,  except  in  dissections  of  the  root,  and  occur  so 
rarely  they  may  be  ignored  in  practice. 

185.  Sometimes  the  horns  of  the  pulp  approach  abnor- 
mally near  the  points  of  the  cusps  of  some  of  the  teeth,  as  in 
the  upper  first  bicuspids,  and  in  the  mesio-buccal  cusp  of  the 
upper  first  molar.  Then  the  pulp  is  more  liable  to  exposure 
in  excavating  carious  cavities. 

PULP    CHAMBERS    OF    THE    DECIDUOUS    TEETH. 

186.  The  pulp  chambers  of  the  deciduous  teeth  are 
proportionally  larger,  and  the  thickness  of  their  walls  less, 
than  those  of  the  corresponding  permanent  teeth.  The  pulps 
are,  in  consequence,  exposed  with  much  less  penetration  of 
tooth  substance,  and,  therefore,  more  liable  to  exposure  from 
caries,  or  in  the  use  of  cutting  instruments.  The  root  canals 
are  generally  larger  than  in  the  permanent  teeth  of  the  same 
denomination,  but  are  of  the  same  general  form.  Also,  the 
same  rules  for  finding  the  root  canals  in  the  permanent 
molars  apply  to  the  deciduous. 

ARRANGEMENT    OF    THE    TEETH. 

187.  The  upper  teeth  are  arranged  in  the  form  of  a 
semi-ellipse,  the  long  axis  passing  between  the  central  inci- 
sors (Fig.  126).  In  this  curve,  the  cuspids  stand  a  little 
prominent,  giving  a  fullness  to  the  corners  of  the  mouth.  In 
different  persons  there  is  much  variation  of  the  form  of  the 
arch  within  the  limits  of  the  normal.  Occasionally  the  bi- 
cuspids and  molars  form  a  straight  line,  instead  of  a  curve, 
and  frequently  the  third  molars  are  a  little  outside  the 
line  of  the  ellipse.  The  incisors  are  arranged  with  their 
cutting  edges  forming  a  continuous  curved  line  from  cuspid 
to  cuspid,  and  this  line  is  continued  over  the  cusps  of  the 
cuspids,  and  the  buccal  cusps  of  the  bicuspids  and  molars  to 
the  distal  surface  of  the  third  molars.  From  the  first  bi- 
-cuspid  to  the  third  molar  the  lingual  cusps  of  these  teeth 


Fig.  126. 


Fig.  128. 


Fig.  129. 


Fig.  130. 


Fig.  126*  (Par.  187).— Arrangement  of  the  Teeth  in  the  Arch.    The  arch  of  the 
uijper  jaw. 

(Par.  210).— The  Teeth  and  the  Grji.s  and  the  Rug.e  of  the  Roof  of  the  Mouth. 
Fig.  128  (Par.  188).— Labio-Lingu.vl  Position  of  the  Incisors  in  Occlusion. 
Fig.  129  (Par.  188).— Bucco-Lingual  Position  of  the  Bicuspids  in  Occlusion. 
Fig.  130  (Par.  188).— Bucco-Lingual  Position  of  the  Molars  in  Occlusion. 


Illustration,  actual  size. 


ARRANGEMENT  OF  THE  TEETH.  133 


form  a  second  line  of  elevations.  Between  these  two,  the 
lingual  and  buccal  cusps,  there  is  a  continuous  but  irregular 
valley,  or  sulcus. 

188.  The  lower  teeth  are  arranged  similarly  (Fig.  134) 
but  on  a  slightly  smaller  curve,  so  that  in  occlusion  the  upper 
teeth  project  a  little  to  the  labial  and  buccal  of  the  lower  at 
all  points  of  the  arch  (Fig.  127).  The  incisors  and  cuspids 
occlude  80  that  the  cutting  edges  of  the  lower  incisors  and 
cusps  of  the  cuspids  make  contact  with  the  lingual  surfaces 
of  the  similar  teeth  of  the  upper  jaw  near  their  cutting 
edges  (Fig.  128).  The  broad  cusped  occluding  surfaces  of 
the  bicuspids  and  molars  of  the  opposing  dentures  rest  on 
each  other  in  such  a  way  that  the  lingual  cusps  of  the  upper 
teeth  fit  w^ith  more  or  less  accuracy  into  the  general  sulcus 
formed  by  the  buccal  and  lingual  cusps  of  the  lower  teeth. 
The  buccal  row  of  cusps  of  the  lower  teeth,  in  a  similar 
way,  are  fitted  into  the  sulcus  formed  by  the  buccal  and 
lingual  cusp  of  the  upper  teeth  (Figs.  129  and  130).  This 
arrangement  is  such  that  when  the  teeth  are  in  occlusion,  it 
leaves  the  buccal  inclines  of  the  buccal  cusps  of  the  upper 
teeth  outside  the  buccal  surface  of  the  lower  teeth  (a).  And, 
also,  leaves  a  ledge  formed  by  the  abrupt  lingual  inclines  of 
the  lingual  cusps  of  the  lower  teeth  along  the  lingual  line  of 
the  occlusion  (6).  This  brings  the  occluding  surfaces  of  the 
teeth  in  the  best  form  of  apposition  for  the  purposes  of 
mastication.  The  forms  presented  to  the  cheek  and  to  the 
tongue  hold  these  soft  tissues  a  little  apart  from  the  actual 
contact  points  of  the  occlusion,  and  thus  prevents  them  from 
being  caught  and  pinched,  or  crushed,  between  the  teeth  in 
act  of  mastication.  In  youth,  while  the  permanent  teeth  are 
taking  their  places,  and  before  the  cusps  are  properly  fitted 
to  the  sulci,  we  often  find  the  cheeks  or  tongue  wounded  by 
being  caught  between  false  contact  points.  With  the  after 
movements  of  the  teeth  by  which  they  are  more  perfectly 
arranged,  this  difficulty  disappears. 


134  ARRANGEMENT  OF  THE  TEETH. 

189.  The  line  from  before  backward  on  which  the 
occlusion  occurs  is  not  quite  a  plain ;  in  the  lower  jaw  it 
presents  a  slight  curve,  or  concavity,  and  in  the  upper  jaw  a 
convexity  (Fig.  127,  c  to  d).  This  concavity  of  the  line  of 
the  occluding  surfaces  of  the  lower  teeth  is  a  little  greater 
than  the  convexity  of  the  upper,  so  that  the  cutting  edges  of 
the  lower  incisors  pass  a  little  beyond,  and  to  the  lingual  of 
the  cutting  edges  of  the  upper  incisors. 

190.  In  the  occlusion,  the  relative  mesio-distal  position 
of  the  particular  teeth  of  the  upper  jaw  to  the  lower  is  im- 
portant (Fig.  127).  At  their  cutting  edges,  the  upper  central 
incisors  are  about  one-third  wider  from  mesial  to  distal  than 
the  lower  centrals.  The  upper  central,  therefore,  occludes 
with  the  lower  central,  and  also  with  from  one-third  to  one- 
half  of  the  lower  lateral  incisor.  The  upper  lateral  occludes 
with  the  remaining  portion  of  the  lower  lateral,  and  the 
mesial  portion  of  the  lower  cuspid.  The  upper  cuspid  is 
usually  rather  broader  from  mesial  to  distal  than  the  lower, 
and  in  occlusion  covers  its  distal  two-thirds  and  about  half 
of  the  lower  first  bicuspid  so  that  its  lingual,  or  triangular 
ridge,  is  between  two  cusps  of  the  lower  cuspid  and  the 
buccal  cusp  of  the  lower  first  bicuspid,  the  point  of  its  cusp 
overlapping  the  lower  teeth.  The  buccal  cusp  of  the  lower 
first  bicuspid  occludes  in  the  space  between  the  upper  cuspid 
and  upper  first  bicuspid.  This  order  is  now  maintained 
between  the  bicuspids.  The  buccal  cusp  of  the  upper  first 
bicuspid  overlaps  (to  the  buccal)  the  space  between  the  two 
lower  bicuspids,  and  its  lingual  cusp  occludes  in  the  sulcus 
between  them,  while  the  buccal  cusp  of  the  lower  second 
bicuspid  occludes  in  the  sulcus  between  the  two  upper  bicus- 
pids. The  cusps  of  the  upper  second  bicuspid  occlude 
between  the  lower  second  bicuspid  and  lower  first  molar. 
The  broad  surfaces  of  the  molars  come  together,  so  that  the 
mesial  two-thirds  of  the  upper  first  molar  covers  the  distal 
two-thirds  of  the  lower  first  molar;  and  the  distal  third  of 


Fig.  127.— Actual  size. 


Fig.  127  (Par.  188).— Arrangement  of  the  Teeth.  Labial  and  buccal  aspect  of 
the  upper  and  lower  teeth  as  arranged  in  the  arch. 

(Par.  197).— The  Alveolar  Process  of  the  Upper  and  Lower  Jaws,  with  the 
Teeth  in  Position. 


ARRANGEMENT  OF  THE  TEETH.  137 


the  uiDjDer  first  molar  covers  the  mesial  third  of  the  lower 
second  molar.  This  brings  the  transverse  ridge  of  the  upper 
molar  between  these  two  lower  teeth.  This  order  is  con- 
tinued between  the  remaining  molars,  but  less  perfectly  as 
the  teeth  are  more  irregularly  formed.  The  upper  third 
molar  is  usually  smaller  than  the  lower  third  molar,  yet  it 
generally  extends  over  its  distal  surface. 

191.  The  long  axis  of  the  upper  incisors  and  cuspids 
are  so  arranged  that  their  crowns  are  inclined  more  or  less 
forward  from  the  perpendicular  position,  or  toward  the  lip, 
and  slightly  toward  the  median  line.  The  mesial  inclination 
is  continued  in  the  bicuspids  and  molars,  diminishing  from 
before  backward,  and  is  usually  lost  at  the  second  or  third 
molar.  As  a  rule,  the  bicuspids  and  molars  of  the  upper 
jaw  are  also  slightly  inclined  toward  the  cheek,  but  in  many 
dentures  this  inclination  is  slight,  or  wanting  in  the  bicus- 
pids and  first  molars  to  re-appear  in  the  second  and  third 
molars,  though  it  ma}^  be  absent  even  in  these  without  neces- 
sary malformation. 

192.  The  lower  incisors  and  cuspids  are  also  inclined 
with  their  crowns  toward  the  lip,  but  in  less  degree  than  the 
upper.  And  even  the  perpendicular  position  of  these  is  not 
inconsistent  with  a  normal  arrangement.  They  have,  how- 
ever, a  mesial  inclination,  but  usually  much  less  than  the 
corresponding  upper  teeth.  The  lower  bicuspids,  within  the 
limits  of  the  normal  arrangement,  vary  considerably  in  their 
inclinations.  Sometimes  they  have  a  strong  mesial  inclina- 
tion, and  at  other  times  they  are  nearly  or  quite  perpendicu- 
lar. In  many  dentures,  they  also  have  a  lingual  inclination, 
but  may  be  perpendicular  or  even  have  a  slight  buccal  incli- 
nation. The  lower  molars  usually  have  a  slight  mesial  and 
lingual  inclination  (Fig.  134).  In  many  examples,  however, 
the  mesial  inclination  is  wanting,  especially  in  the  second 
and  third  molars. 

193.  All  the  teeth  are  a  little  broader  from  mesial  to 


138  ARRANGEMENT  OF  THE  TEETH. 

distal  at  or  near  the  occluding  surfaces  than  at  their  necks. 
Therefore,  when  arranged  in  the  arch  with  their  proximate 
surfaces  in  contact,  there  is  a  considerable  space  between 
their  necks  (Fig.  127).  These  are  known  as  the  inter-proxi- 
mate, or  V-shaped,  spaces.  The  sharp  angle  or  apex  of  the 
V-form  is  toward  the  occluding  surface,  or  at  the  contact 
point  of  the  proximation,  and  the  open  end  or  base  is  at  the 
crest  of  the  alveolar  process.  I  n  normal  conditions  this  space 
is  filled  by  the  soft  tissues,  or  gums  (136).  The  average  arch 
measures  about  127  millimeters  (5  inches)  from  the  distal  sur- 
face of  the  right  third  molar  to  the  distal  surface  of  the  left  third 
molar,  following  the  curve  of  the  arch.  This  represents  the 
average  mesio-distal  measurement  of  the  crowns  of  the  teeth 
of  the  upper  jaw  taken  collectively.  The  average  measure- 
ment of  the  teeth  at  their  necks  is  about  89  millimeters  (3.5 
inches).  The  remaining  38  millimeters  (1.5  inches)  repre- 
sent the  average  sum  of  the  inter-proximate  spaces  taken 
collectively. 

194.  On  account  of  differences  in  the  conformation  of 
the  crowns  and  the  inclination  of  the  teeth,  the  inter-proxi- 
mate spaces  vary  much  in  width  in  different  dentures.  They 
are  much  wider  between  bell-crowned  teeth  than  between 
thick-necked  teeth  ;  but  some  inter-proximate  space  exists  in 
every  normal  denture.  When  the  crowns  of  the  incisors  and 
cuspids  are  much  inclined  toward  the  lip,  the  necks  of  the 
teeth  form  a  smaller  circle  than  the  line  of  the  contact  points 
of  the  proximation,  and  in  this  way  the  inter-proximate 
spaces  may  be  considerably  narrowed.  Generally,  the  inter- 
proximate  space  is  wide  between  the  necks  of  the  central 
incisors.  The  suture  joining  the  maxillary  bones  passes  be- 
tween the  roots  of  these  teeth,  and  they  are  somewhat  farther 
apart  than  the  roots  of  central  and  lateral  incisors,  or  those 
of  the  lateral  incisor  and  the  cuspid.  Therefore,  in  these 
latter,  the  inter-proximate  spaces  are  of  less  width.  Between 
the  bicuspids  the  inter-proximate  spaces  are  wider  at  the 


ARRANGEMENT  OF  THE  TEETH.  139 

necks  of  the  teeth  than  between  the  anterior  teeth,  on  account 
of  the  proportionally  broader  crowns.  The  widest  inter-proxi- 
mate spaces  are  usually  between  the  necks  of  the  molars. 

195.  The  points  of  the  proximate  contact  in  the  best 
formed  arches  are  very  near  the  occluding  surfaces  of  the 
teeth.  In  imperfectly  developed  teeth,  in  which  the  crowms 
are  much  rounded  toward  the  occluding  surfaces,  the  con- 
tact point  is  more  toward  the  gingival.  In  the  incisors  and 
cuspids  it  is  in  direct  line  with  the  cutting  edges.  In  the 
bicuspids  the  contact  is  with  the  buccal  angles  and  in  line 
with  buccal  cusps.  The  mesial  and  distal  flattened  surfaces 
of  these  teeth  converge  to  the  lingual  to  such  an  extent  that, 
though  they  are  arranged  in  arch  form,  the  contact  points  re- 
main on  .the  buccal  angles.  In  many  excellent  dentures 
there  is  a  decided  inter-proximate  space  opening  to  the  lin- 
gual, but  in  thick-necked  teeth  and  those  of  a  more  rounded 
contour,  the  contact  points  are  often  more  toward  the  lingual, 
and  there  is  no  appreciable  lingual  inter-proximate  space.  In 
the  molars  the  contact  jDoints  as  a  rule  are  removed  rather 
more  to  the  lingual,  but  still  in  the  best  formed  dentures 
they  will  be  found  nearly  in  line  with  the  buccal  cusps. 
Between  the  upper  first  and  second  molars,  the  contact  point 
is  often  extended  toward  the  lingual  by  the  prominent  disto- 
lingual  cusp  of  the  first  molar;  and,  even  when  otherwise, 
the  general  rounding  of  the  distal  surfaces  of  the  upper 
molars  often  brings  the  contact  point  near  the  middle  line  of 
the  teeth.  In  lower  first  molars  the  large  distal  cusp  brings 
the  contact  point  with  the  second  molar  close  to  the  buccal 
side,  wdth  a  considerable  lingual  inter-proximate  space.  If 
the  distal  cusp  is  small  the  contact  point  is  usually  extended 
toward  the  lingual,  often  as  far  as  half  the  labio-lingual 
breadth  of  the  teeth.  Between  the  second  and  third  molars 
the  contact  point  is  most  frequentl}^  near  the  central  line  of 
the  teeth.  l_In  the  best  formed  dentures  the  form  of  the 
proximate  contact  is  such  as  to  prevent  food  from  being^ 


140  THE    ALVEOLAR    PROCESS    AND    ALVEOLI. 

crowded  between  the  teeth  in  mastication ;  and,  therefore, 
such  as  to  keep  these  spaces  clean  and  the  inter-proximate 
gingivus  in  health.  But  many  faulty  forms  are  met  with 
which  allow  food  to  leak  through  into  the  space  and  crowd 
the  gum  away,  forming  a  pocket  for  the  lodgment  of  debris, 
giving  opportunity  for  decomposition,  and  resulting  in  caries 
of  the  proximate  surfaces,  or  disease  of  the  gum  and  peri- 
dental membrane.  Exceptionally,  cases  are  met  with  in  which 
the  teeth  stand  so  widely  apart  that  the  spaces  are  self-clean- 
ing. The  form  of  the  inter-proximate  spaces  is  very  vari- 
able. ''It  is  best  studied  in  skulls  in  which  the  teeth  are  all 
present,  and  by  careful  consideration  of  the  forms  of  thi 
proximate  surfaces  of  the  teeth,  together  with  their  relative 
positions. 

THE    ALVEOLAR    PROCESS    AND    ALVEOLI. 

196.  The  alveolar  process  is  the  projecting  portion  of 
the  maxillary  bones  within  which  the  roots  of  the  teeth  are 
lodged  in  alveoli,  or  sockets,  accurately  fitted  to  their  sur- 
faces (Figs.  131  and  132).  The  form  of  the  alveolar  process 
seems  to  depend  on  the  teeth,  the  conformation  of  their 
roots,  and  their  arrangement  in  the  arch.  If  any  teeth  are 
misplaced,  or  from  any  cause  stand  out  of  the  regular  and 
normal  line,  the  alveolar  process  is  formed  about  their  roots 
in  this  irregular  position.  Also,  when  teeth  are  lost,  the  al- 
veolar process  mostly  disappears  by  absorption,  and  the  re- 
maining portions  of  the  alveoli  are  filled  with  bone. 

197.  Normally,  the  alveolar  process  envelops  the  roots 
of  the  teeth  to  within  a  short  distance  of  the  gingival  line 
(Figs.  127  and  133),  varying  from  one  to  three  millimeters  in 
the  young  adult.  This  distance  increases  somewhat  with 
increasing  age.  The  margins  of  the  process  are  reduced  to 
a  thin  edge  about  the  necks  of  the  teeth  on  both  the  labial 
and  lingual  sides  of  the  incisors  and  cuspids  of  the  upper 
jaw.     About  the  lingual  sides  of  the  necks  of  the  bicuspids 


Fig.  131. 


Fig.  132. 


Fig.  133. 

Fig.  131  *  (Par.  196).— Section  op  the  Alveolar  Peocess  and  Roots  of  the  Teeth 
OF  the  Upper  Jaw,  showing  the  roots  of  the  teeth  in  position. 

Fig.  132  *  (Par.  196).— Horizontal  Section  of  the  Alveolar  Process  and  Roots  of 
the  Teeth  of  the  Lower  Jaw,  showing  the  roots  of  the  teeth  in  position. 

Fig.  133*  (Par.  197).— The  Teeth  and  Lingual  Portion  of  the  Alveolar  Process 
OP  THE  Upper  Jaw,  and  the  Bones  of  the  Roof  op  the  Mouth. 


*  Illustration,  actual  size. 


THE    ALVEOLAR    PROCESS    AND    ALVEOLI.  143 

and  molars  the  margins  are  also  reduced  to  a  thin  edge,  be- 
coming slightly  thickened  about  the  second  and  third  molars, 
especially  of  the  latter.  On  the  buccal  sides  of  these,  a  thick- 
ening of  the  immediate  margin  of  the  process,  in  the  form  of 
&  marked  ridge,  begins  about  the  first  or  second  bicuspid, 
more  commonly  between  these  two,  and  extends  to  the  distal 
of  the  third  molar  (Fig.  127,  <z).  This  ridge  varies  in  difi:erent 
examples,  from  a  very  slight  thickening  of  the  immediate 
margin,  to  a  thickness  of  two  or  three  millimeters.  It  forms 
a  margin  standing  squarely  out  from  the  necks  of  the  teeth. 
The  process  then  thins  away  so  that,  in  many  instances,  the 
buccal  roots  of  the  teeth,  especially  the  mesial  root  of  the 
first  molar,  have  but  a  thin  covering  of  bone. 

198.  Anteriorly,  the  bony  covering  of  the  roots  of  the 
incisors  presents  much  variety.  In  some  examples,  the 
middle  portion  of  the  roots  has  but  a  slight  covering  of 
bone,  but  more  generally  it  is  progressively  thickened  from 
the  neck  to  the  apex.  The  roots  of  the  cuspids  are  prominent 
toward  the  lip,  and,  for  most  of  their  length,  have  only  a 
thin  bony  covering,  and  this  forms  a  ridge  along  the  line  of 
the  root,  which  may  easily  be  traced  with  the  finger  through 
the  soft  tissues  of  both  the  gum  and  lij^.  In  many  instances, 
the  bony  covering  is  entirely  wanting  for  a  little  space  near 
the  middle  of  the  length  of  the  root  of  the  cuspid,  the  buccal 
root  of  the  first  bicuspid,  the  mesial  root  of  the  first  molar, 
and,  occasionally,  of  other  teeth. 

199.  On  the  lingual  side  of  the  upper  teeth  (Fig.  133), 
the  progressive  thickening  of  the  alveolar  process,  from  the 
gingivus  toward  the  apex  of  the  root,  is  much  greater ;  so 
that  the  roots  of  the  teeth  seem  to  lie  toward  the  labial  and 
buccal  side  of  the  alveolar  process  (Fig.  131).  Even  the  large 
lingual  root  of  the  first  upper  molar,  diverging  strongly  to 
the  lingual,  seldom  forms  a  ridge  or  prominence  of  the  pro- 
cess covering  its  lingual  surface. 

200.  The  anterior  palatine  foramen  is  in  the  median 


144        THE  ALVEOLAR  PROCESS  AND  ALVEOLI. 

line,  just  behind  the  central  incisors  (Fig.  133).  It  is  fannel- 
shapecl  with  a  broad  opening  to  the  palatine  surface  of  the 
bone.  The  bone  is  often  quite  thin  between  this  and  the 
roots  of  the  central  incisors.  The  posterior  palatine  artery 
runs  in  a  deep  groove  in  the  surface  of  the  bone,  very  close 
to  the  apex  of  the  lingual  roots  of  the  upper  third,  and  the 
upper  second  molar.  This  artery  is  occasionally  wounded, 
or  cut,  in  eiforts  to  extract  the  roots  of  these  teeth. 

201.  In  the  lower  jaw,  the  immediate  margins  of  the 
alveolar  process,  on  the  labial  sides  of  the  incisors,  are  rather 
thicker  than  in  the  upper  jaw,  often  amounting  to  a  decided 
ridge.  This,  however,  thins  away  rapidly,  so  that  the  middle 
portion  of  the  roots  has  but  a  thin  covering  of  bone.  At  the 
cuspid,  the  margin  of  the  process  is  very  thin,  but  a  gingival 
ridge,  corresponding  with  that  of  the  upper  jaw,  though  not 
so  prominent,  begins  at  about  the  first  or  second  bicuspid 
and  runs  to  the  second  molar.  This  thins  away  over  middle 
of  the  length  of  the  roots  of  the  bicuspids  and  first  molar. 
At  the  second  lower  molar,  the  rising  of  the  external  oblique 
ridge  for  the  formation  of  the  anterior  border  of  the  coronoid 
process  (Fig.  127,  6),  causes  a  thickening  of  the  buccal  bony 
covering  of  the  root,  while  at  the  third  molar  this  ridge 
rises  to  a  level  with  the  gingival  margin  of  the  process, 
making  the  bony  covering  on  the  buccal  side  of  the  root 
about  one-fourth  of  an  inch  thick  (Fig.  132).  This  is  of  im- 
portance with  reference  to  the  extraction  of  the  roots  of  this 
tooth.  Indeed,  the  second  and  third  molars  of  the  lower 
jaw  are  fixed  in  alveoli,  hollowed  out  in  the  lingual  side  of 
the  body  of  the  bone  rather  than  in  a  process  or  ridge  on  the 
bone,  as  with  the  teeth  anterior. 

202.  On  the  lingual  side  of  the  lower  anterior  teeth,, 
the  immediate  gingival  border  of  the  alveolar  process  is  a 
smooth  thin  edge,  and  the  covering  of  bone  over  the  roots 
progressively  thickens  toward  their  apexes.    In  this  portion,, 
the  process  is  high,  and  the  labio-lingual  thickness  is  only 


Fisr.  134. — Actual  size. 


sS^J\*vS5?S', 


Fig.  136.— Actual  size. 


Fig.  131  (Par.  202}. — Lower  Teeth  and  Maxilla,  as  seen  from  above. 
Fig.  136  (Par   210)  —The  Labial  and  Buccal  Aspect; of^the  Teeth\4.nd  Gums  of 
THE  Upper  Jaw. 


THE    AVEOLAR   PROCESS   AND*  ALVEOLI.  147 

sufficient  to  envelop  the  roots  of  the  teeth  and  give  them 
support  (Figs.  134  and  135).  From  the  first  bicuspid  back- 
ward the  height  of  the  process  diminishes  rapidly,  and  the 
line  of  the  dental  arch,  and  of  the  alveoli  of  the  teeth,  passes 
diagonally  across  the  line  of  the  curve  of  the  body  of  the 
bone  from  the  buccal  side  at  the  first  bicuspid  to  the  lingual 
side  at  the  third  molar,  and  sinks  into  the  body  of  the  bone 
(Figs.  134  and  135).  The  immediate  gingival  border  re- 
mains thin  as  far  as  the  first  or  second  molar,  but  the  bony 
covering  of  the  roots  is  rapidly  thickened  toward  their  apexes. 

203.  This  is  caused  largely  by  the  thickening  of  the 
body  of  the  bone,  produced  by  the  rise  of  the  mylohyoid 
ridge  (Fig.  135,  a),  which  begins  in  front  below  the  apexes 
of  the  roots  and  rises  progressively  backward  nearly  to  the 
gingival  border  of  the  alveolus  at  the  third  molar.  The 
greatest  thickness  is  over  the  lingual  side  of  the  apical  half 
of  the  roots  of  the  second  molar,  and  of  the  crossing  of  the 
lingual  side  of  the  coronal  half  of  the  roots  of  the  third 
molar.  At  the  third  molar  this  ridge  is  thinner,  and  at  the 
distal  angle  often  very  slight,  while  the  lingual  covering  of 
the  roots  of  the  tooth  may  be  very  thin  below  this  ridge. 
Therefore,  it  is  usually  easy,  when  necessary  in  extracting, 
to  force  the  roots  of  the  lower  third  molar  to  the  lingual 
and  distal  with  a  lever  suitably  arranged  against  the  crown 
of  the  second  molar,  as  with  the  Physic's  forcep,  or  an 
elevator. 

204.  The  gingival  margin  of  the  septi  of  the  alveoli  of 
the  roots  of  the  anterior  teeth  are  rounded  from  labial  to 
lingual,  but  this  diminishes  rapidly  from  the  cuspid  back- 
ward. Between  the  molars  it  is  a  straight  line,  or  presents 
but  a  slight  concavity,  so  that  the  highest  points  of  the 
gingival  border  of  the  process  are  on  the  buccal  and  lingual 
surfaces,  or  at  the  angles,  of  the  necks  of  these  teeth,  which 
is  important  in  fitting  bands  of  crowns  or  any  similar 
processes. 


148  THE   PERIDENTAL   MEMBRANE. 

205.  The  alveolar  process  is  composed  of  an  outer  and 
an  inner  plate  of  moderately  compact  bone,  and  between 
these,  -very  open  cancellous  or  spongy  bone ;  so  that  in  young 
persons  the  process  may  be  forced  more  or  less  to  one  side, 
or  bent  out  of  position,  without  definite  fracture.  The  outer 
compact  plate  forms  the  outer  surface  of  the  bone,  and  the 
inner  plates  line  the  alveoli  of  the  teeth.  These  latter  are 
very  thin,  and  supported  on  all  sides  by  the  cancelous 
structure.  In  the  lower  jaw  the  substance  of  the  bone  is 
more  compact  and  stronger  than  in  the  upper,  especially 
about  the  molar  teeth,  where  the  alveoli  are  in  the  substance 
of  the  body  of  the  bone. 

THE    PERIDENTAL    MEMBRANE. 

206.  The  peridental  membrane  invests  the  roots  of  the 
teeth  from  the  gingival  line  to  the  apexes  of  the  roots  like  a 
sack.  It  lines  every  part  of  the  alveoli,  and,  passing  over 
the  gingival  margins,  is  continuous  with  the  periosteum  and 
gums  covering  the  outer  plates  of  the  alveolar  processes.  It 
is  one  membrane  attached  on  one  side  to  the  root  of  the 
tooth,  and  on  the  other  to  the  inner  wall  of  the  alveolus.  It 
is  composed  of  connective  tissue  which  supports  an  abundant 
supply  of  blood  vessels,  nerves  and  lymphatics.  With  these 
are  intermingled  strong  fibers  of  white  fibrous  tissue  which 
pass  from  the  cementum  of  the  root  of  the  tooth  to  the  bony 
walls  of  the  alveolus.  The  ends  of  these  are  built  firmly 
into  each,  forming  a  strong  attachment  of  the  root  to  its  al- 
veolus. In  childhood  and  youth,  this  membrane  is  compar- 
atively thick,  and  allows  considerable  motion  of  the  tooth  in 
its  socket.  As  age  advances,  it  becomes  thinner  and  the 
motions  of  the  teeth  are  more  restricted.  A  bundle  of 
nerves  and  one  or  more  arteries  enter  the  alveolus  near  the 
apex  of  the  root  (the  apical  space),  and,  subdividing,  several 
arterial  twigs  and  nerve  bundles  pass  toward  the  gingivus ; 
while  others  enter  the  apical  foramen  and  pass  to  the  pulp 


Fig.  135.— Actual  size. 


Fig.  135  (Par.  202).— Lingual  Surface  of  the  Left  Half  of  the  Lower  Maxilla 
AND  Teeth,    a,  Mylo-hyoid  ridge ;  b,  inferior  dental  foramen. 


THE    GUMS.  151 


of  the  tooth.    At  the  gingivus,  the  blood-vessels  become  con- 
tinuous with  those  of  the  periosteum  and  gums."--' 


THE  GUMS. 


207.  The  gums  are  the  soft  tissues  covering  the  alveolar 
processes  and  investing  the  necks  of  the  teeth.  They  are 
composed  of  connective  tissue  containing  many  white  fibres 
intermingled,  forming  a  firm  membranous  mass,  continuous 
with  the  periosteum  beneath  and  peridental  membrane  at 
the  necks  of  the  teeth.  They  are  covered  with  a  strong 
outer  coat  of  squamous  epithelium.  They  are  richly  supplied 
with  blood-vessels  and  nerves ;  but,  under  normal  conditions, 
they  are  not  very  sensitive  to  pressure  or  moderate  violence, 
but,  in  pathological  conditions  they  may  become  very  sen- 
sitive. 

208.  On  the  labial  and  buccal  side  of  the  alveolus,  the 
gums  (Fig.  135)  are  thin  and  firm  near  the  necks  of  the  teeth 
and  strongly  attached  to  the  periosteum.  As  they  pass  from 
the  necks  of  the  teeth  toward  the  base  of  the  alveolar  ridge 
they  become  softer  and  loose  their  attachment  to  the  perios- 
teum, and  become  merged  into  the  buccal  mucous  membrane 
of  the  lips  and  cheeks.  In  the  passage  from  the  gums  to 
these  mucus  surfaces  several  loose  folds  are  formed,  the 
most  notable  being  the  frenum  labium  of  the  upper  jaw  at 
the  median  line,  passing  from  near  the  inter-proximate  space 
of  the  central  incisors  to  the  median  line  of  the  upper  lip. 
A  similar,  though  less  prominent  fold  connects  the  median 
line  of  the  lower  lip  with  the  gums.  Occasionally,  folds  of 
less  prominence  are  seen  in  the  neighborhood  of  the  bicuspids 
and  first  molars. 

209.  On  the  lingual  side  of  the  arch  in  the  lower  jaw, 
the  conditions  are  much  the  same.     The  gums  are  firmly 


*  For  the  details  of  this  subject  the  student  is  referred  to  the  author's 
treatise  on  "The  Histological  Character  of  the  Periosteum  and  PeridentaL 
Membrane," 


152  THE    GUMS. 


adherent  to  the  periosteum  near  the  teeth,  but  lower  down 
are  merged  into  the  mucous  membrane  of  the  floor  of  the 
mouth.  The  median  line  of  the  tongue  is  connected  with 
the  median  line  of  the  gums  by  a  strong  fold,  known  as  the 
frenum  linguse.  As  an  abnormal  congenital  condition  this 
is  sometimes  connected  so  near  the  tip  of  the  tongue  as  to 
prevent  its  protrusion  over  the  teeth,  constituting  the  condi- 
tion known  as  "  tongue-tied."  This  is  generally  corrected 
by  the  muscular  efforts  of  the  tongue,  which  stretch  the 
membrane  sufficiently  to  accommodate  its  motions. 

210.  On  the  lingual  side,  in  the  upper  jaw,  the  gums 
(Fig.  136)  are  usually  of  greater  extent  and  thicker.  They 
cover  the  entire  roof  of  the  mouth,  to  the  conjunction  of  the 
hard  and  soft  palate,  as  a  hard  dense  layer.  In  the  anterior 
portion,  a  series  of  irregular  ridges,  known  as  the  rugse, 
radiate  from  the  median  line  toward  both  sides,  stopping 
short  of  the  gingivae.  In  a  large  collection  of  examples 
almost  innumerable  forms  of  these  rugse  may  be  noted. 

211.  The  gingivae,  or  gingivus,  is  that  ]3ortion  of  the 
gum  tissue  investing  the  neck  of  the  tooth  crownwise  from 
the  attachment  of  the  peridental  membrane  at  the  gingival 
line.  It  is  also  termed  the  free  margin  of  the  gum.  The 
length  of  the  gingivae,  from  the  attachment  to  the  neck  of 
the  tooth,  varies  in  different  teeth  in  the  same  mouth,  and  in 
different  adults,  from  about  one  to  about  four  millimeters.  It 
is  often  much  greater  in  young  persons,  but  the  length  usually 
diminishes  as  age  advances.  The  free  margin  fits  around  the 
neck  of  the  tooth  closely  ;  but  a  thin,  flat  instrument  is  easily 
passed  between  it  and  the  tooth  to  the  attachment  at  the 
gingival  line.  As  the  gingival  line  of  the  tooth  is  at  the 
border  of  the  enamel,  or,  at  the  junction  of  the  enamel  and 
cementum,  it  follows  that  the  gingivae  inclose  the  immediate 
border  of  the  enamel,  and  cover  this  part  of  the  crown  of 
the  tooth.  In  young  persons,  we  often  see  one-half  of  the 
length  of  the  crowns  of  the  teeth  buried  in  the  gingivae,  even 


THE   GUMS.  153 


after  the  teeth  are  regarded  as  fully  in  place.  As  age  ad- 
vances, the  gingivae  become  shorter,  showing  more  of  the 
own,  and  finally  recede  to  very  near  the  gingival  line. 
212.  The  gingivae  also  fill  the  inter-proximate  spaces  in 
the  form  of  septi  passing  between  the  teeth  from  labial,  or 
buccal,  to  lingual.  This  portion  of  the  gingivus  is  much 
longer  than  that  on  the  labial  and  lingual  surfaces  of  the 
teeth  (Fig.  136).  In  normal  conditions  it  reaches  from  the 
gingival  line  to  the  contact  point  between  the  teeth,  com- 
pletely filling  the  space  and  preventing  accumulation  of 
debris.  The  form  presented  by  the  gingivae  on  the  labial 
and  buccal  surfaces,  is  a  series  of  imperfect  semi-circles  with 
the  concavity  toward  the  occluding  surfaces  of  the  teeth,  and 
with  the  points  of  junction  of  these .  extending  into,  and  fill- 
ing the  inter-proximate  spaces  (Fig.  136).  On  the  lingual 
side  of  the  arch,  the  conditions  are  much  the  same,  but  the 
points  of  the  gingivae  between  the  teeth  are  less  prominent 
(Fig.  126).  As  age  advances  and  the  gingivae  recede  toward, 
or  even  to,  the  gingival  line,  the  septi  of  soft  tissue  some- 
times fail  to  fill  the  inter-proximate  spaces.  This  may  in- 
duce pathological  conditions  by  afi'ording  space  for  lodgment 
of  debris  in  pockets,  which  favors  fermentation.  A  like 
condition  is  also  induced  frequently  by  a  faulty  form  of 
proximate  contact,  which  allows  food  to  be  forced  into  the 
inter-proximate  space,  and  break  down  the  gum  septum  by  its 
pressure. 


INDEX. 

THE  NUMBERS  REFER  TO  THE  PARAGRAPHS. 

Alveolar  process 196 

"            "      — at  the  buccal  side  of  the  lower  third  molar 201 

"            "      — bone  forming  the 205 

"            "      —buccal  ridge 197 

"            "      — lower  labial  portion 201 

"            "      — lower  lingual  portion 202 

"            "      — relation  of  the  mylohyoid  ridge 20S 

"            "      — relation  of  the  oblique  ridge 201 

"            "      — septi  of  the 204 

"            "      — upper  labial  portion 198 

"            "      — upper  lingual  portion 199 

Alveoli 196 

"      — relation  of  the  roots  of  the  teeth 197 

Angles — how  named 6 

Apical  foramen 153 

Apex  of  the  root  defined 3 

Arrangement  of  the  teeth , 187 

Bell  crowned  teeth 14 

"             "           "    — inter-proximate  spaces 194 

Bicuspids 41 

"        buccal  surface  of  the  lower  first  .• 57 

"            «            "        "            "      second 63 

"            "            "        "        upper  first 46 

"            "             "         "            "       second 52 

"        — distal  surface  of  the  lower  first 58 

"                "           "        "            "      second 64 

"                "           "         "        upper  first 49 

"                "           "        "            "      second 52 

"        — grooves  of  lower  first 54-55 

«                 "        "      "      second 62 

"                  "        "  upper  first 45 

«                  «         "       "      second 51 

"        — lingual  surface  of  the  lower  first 59 

"                  "             "         "            "      second 63 

"                  «            "         "        upper  first 47 

"                 "            "        "            "      second 52 


11  INDEX. 

Bicuspids — mesial  surface  of  the  lower  first 58 

"                 "            "        "            "     second 64 

"                 "            "         "        upper  first 48 

"                 "            "        "            "      second 52 

"        — occluding  surface  of  lower  first 54 

"                    "            "         "        "    second 62 

"                    "            "         "     upper  first., 42 

"                    "            "        «        "     second 51 

"        — plan  of  the  formation 41 

"        — root  of  lower  first 61 

"              "     "        "     second 65 

"              "     "     upper  first  50 

"              "    "        "      second 53 

"        — ridges  of  lower  first 54-56 

"      '         "      "        "     second 62 

"                "      "    upper  first 43-44 

"                "       "        "      second 51 

"        — lower  first 54 

"                "      second 62 

"        — upper  first 42 

"                "      second 51 

Characteristics  common  to  all  of  the  teeth 3 

Cingulum 18 

Color  of  the  deciduous  teeth 133 

Contact,  proximate 195 

Crown,  surfaces 3 

Crowns  of  the  teeth 3 

"       "       "    lower  incisors 7 

Crowns  of  the  deciduous  teeth 130 

Cutting  edge  of  the  incisors 7 

Curvature  of  the  gingival  line 3 

Cusp  defined 8 

Cuspid,  lower 38 

"          "      —ridges 39 

"          "      — similarity  to  the  upper 38 

"          "      —surfaces 38-39 

"          "      —root 40 

"       upper 33 

"           "      — distal  surface 36 

"          "      — labial  surface 33 

"          "      — labial  ridge 33 

"           "      — lingual  surface 34 

"          "      — mesial  surface 35 

"          "     —ridges 34 


INDEX.  Ill 

Cuspid,  upper — root 37 

Deciduous  first  molars  a  distinct  class 129 

"         second  molars 129 

"         teeth 128 

"            "    — by  what  teeth  succeeded , 129 

"            "    — buccal  surfaces 132 

«            "     —color 133 

"            "    — lingual  surfaces 132 

"            "     — crowns 130 

"            "    —necks 131 

"            "    —number 128 

"            "     —roots 151 

"         molars — lower  first  buccal  surface 148 

"               "             "        "     bucco-gingival  ridge 148 

"              "            "         "     cusps 143 

"              "            "        "    distal  surface 149 

"              "            "        "    fossje 141 

"              "             "         "    grooves 142 

"               "            "         "     lingual  surface 149 

"              "            "        "    lobes 142 

"              "             "        "    mesial  fossa 147 

"              "             "         "     mesial  surface 149 

"              "             "         "     occluding  surface 141 

"              "            "         "     principal  fossa 146 

"              "            "        "    ridges 143 

"              "        upper  first  buccal  surface 138 

"              "            "        "    bucco-gingival  ridge 138 

"              "            "        "    cusps 136 

"               "            "         "     distal  surface. 140 

"              "            "        "    grooves 135 

"              "            "        "    lobes 135 

"              "            "        "    lingual  surface 140 

"              "            "        "    mesial  surface 140 

"              "            "        "    occluding  surface 134 

"              «            "        "    ridges 136 

Dental  arch 187 

Developmental  grooves  defined 11 

"                    "       of  the  incisors  and  cuspids 21 

"                    "       of  the  molars 98 

"                   "       lines  defined 11 

"                    "       lines  of  the  incisors  and  cuspids 21 

"                    "       lines  of  the  first  upper  molar 98 

Dissections 158 

"          instruments  necessary 158 


IV  INDEX. 

Dissections  of  the  bicuspids 166 

"          of  the  incisors 159 

"          of  the  lower  molars 179 

"          of  the  upper  molars 171 

fissure  defined 11 

Fissures,  how  formed 21 

Foramen,  apical 163 

Fossa  defined 10 

Frenum  labium ... 208 

Frenum  linguae 209 

Oingivse 211 

"   ■    — inter-proximate  spaces 212 

Gingival  groove  and  fissure  of  the  upper  lateral  incisor 26 

"        line,  curvature  of  the , 3 

"          "   defined 3 

"          "    of  the  upper  central  incisor 20 

"        ridge  of  central  incisor 18-21 

"           "      of  the  cuspid 84 

Groove,  defined 11 

"            "       developmental 11 

"            "       sulcate 11 

''            ''       supplemental 12 

Oums 207 

"    labial  and  buccal 208 

"     lingual  of  lower  jaw 209 

"        "         "   upper  jaw 210 

"     of  what  composed 207 

Incisors,  lower 29 

"            "    — developmental  lines 30 

''            "    — difierence  between  central  and  lateral 29 

"            "     —distal  surface 30 

*'            "    — form  of  crown 29 

"            "    —labial  surface 29 

"            "     — lingual  surface 30 

"            "     — lingual  ridge 30 

"            "    — mesial  surface 30 

"            "    —roots 31 

"        upper  central 16 

"             "          "      — distal  surface 19 

"            "          "      — developmental  lines  or  grooves 21 

"            "          "      —fissures 21 

"            "          "      — form  of  crown 16 

"            "          "      — gingival  fissure 21 

"            "           "      —gingival  line 20 


INDEX.  V 

Jncisors,  upper  central — gingival  ridge 18 

"            "          "      — labial  surface  17 

"            "          "      —lingual  fossa 18 

"             "           "      —lingual  pit 21 

"             "           "      — lingual  surface 18 

"             "           "      — lobes  of  crown 21 

"            "          "      — marginal  ridges 18 

"            "           "      — mesial  surface 19 

"             "          "      —root 22 

"            "       lateral 23 

"            "           "      —distal  surface 25 

"            "           "       — division  of  lingual  lobe 26 

"            "           "       —failure  of  lingual  lobe 26 

"            "          "      — gingival  fissure 26 

"            "           "      — general  form  of  crown 23 

"             "           "      — how  different  from  the  central 23 

"            "           "      —labial  surface 24 

"            "           "      —lingual  pit 26 

"            "           "      — lingual  surface 26 

"            "           "      — mesial  surface 25 

"            "           '■      — marginal  ridges 26 

"             "           "      —root 27 

Inclination,  mesial — of  the  lower  teeth 192 

"                "     — of  the  upper  teeth 191 

Inter-proximate  spaces 193 

"     defined 13 

"                   "     — relation  to  the  forms  of  the  teeth 194 

Introduction 1 

Lines — developmental 11 

"                    "            — of  the  incisors 21 

Lobes  of  the  incisors 21 

Lingual  pit  of  the  lateral  incisor 26 

Linguo-gingival  groove 21 

Long  cusped  teeth 14 

Lobes  of  the  incisors 21 

Man's  diet 1 

Marginal  ridges 9 

Mesial  surface  defined 5 

Measurements  of  the  teeth 15 

"    —tables  of 15 

Mesial  inclination  of  the  lower  teeth 191,  192 

"              "            "        upper     " 191,  192 

Molar,  lower  first 96 

"          "        "  —buccal  pit 104 


VI  INDEX. 

Molar,  lower  first — buccal  groove 104 

"  "        "  — buccal  surface 104 

«  «        " —central  fossa 98 

"  "        "—cusps 100,101,102 

"  "        "  — developmental  grooves 98 

"  "        " —distal  sm  face 107 

"—fissures 103 

"  "        "—grooves 98 

"  "        "  —lingual  surface 105 

"  "         "  — mesial  surface ■ 106 

"  "        "  — mesial  supplemental  fossa 101 

"  "        "  — occluding  surface 96,  98 

"—pits 108 

"  "        "  — triangular  ridges 102 

"—root 108 

"  "    second 109 

"  "        "    —buccal  surface 115 

"  "         "    —cusps 112 

"  "        "    — developmental  grooves , Ill 

"  "        "    —distal  surface 118 

"  "         "    —fissures 114 

"  "        "    —lingual  surface 116 

"  "         "    —lobes Ill 

"  "        "    — mesial  surface 117 

"  "         "    — occluding  surface   1]0 

"  "        "    —pits 112 

"  "         "    —root.... 119 

"  "        "    — supplemental  fossae 112 

"  "         "    — supplemental  grooves. 112 

"  "        "    — transverse  ridges 112 

"  "        "    — triangular  ridges 112 

"  "        "    — variations  of  form 113 

"  "     third 120 

"  "        "    — buccal  surface 125 

"  "        "    —distal  surface 126 

«  «        «    — fivelobed 124 

"        "    — fourlobed 121 

"  "        "     —grooves 122 

"  "        "    —lingual  surface 126 

"  "        "    — marginal  ridges 122 

"  "         "     — mesial  surface 126 

"  "         "    —root 127 

"  "         "     — supernumerary  cusps 123 

"  "        "    — supplemental  fossae 121 


INDEX.  vn 

Molars,  triangle,  typical  forms 173 

Molars 66 

— number  and  names 66 

—upper 67 

Molar,  upper  first 68 

"        "  — buccal  surface 78 

"         "  — calcification  of  lobes 69 

"        "  —cusps 71,72,73,74 

"        "  — distal  surface 81 

"        " —fifth  lobe 70 

"         "  — fossEe 68 

"        "  — grooves 68 

"         "  — lingual  surface 79 

"        "  —lobes 68 

"         "  — mesial  surface 80 

"        "  — occluding  surface 68 

"        "  — oblique  ridge 75 

"        "  —ridges 71,  72,  73 

''    second , 86 

"         "     — abnormal  forms 87 

"         "    — buccal  surface 88 

"         "    — central  fossa 86 

"         "     —distal  fossa 86 

"         "    — distal  surface 88 

"        "     — form  of  neck 89 

"         "    — linjjual  surface 88 

"         ''    — mesio-buccal  ridge 89 

"        "    — mesial  surface 88 

"        "    — occluding  surface 86 

"        "    —roots 90 

"        "     — three  cusped 86 

"        "    — variations  of  the  disto-lingual  lobe 86 

"      third 91 

"         "    — buccal  surface 93 

"         "     — distal  surface 93 

"         "     — disto-lingual  cusp 91 

"         "    — irregular  forms 91 

"        "    — lingual  surface 93 

"        "    — mesial  surface 93 

"        "    —multiple  roots 94 

"        "    — occluding  surface 91 

"        "    —root 94 

"        "    — three  cusped 91 

"         "    — variations  of  form 91 


viii  INDEX. 

Neck  of  a  tooth  defined 3 

Number  of  teeth  of  man 2 

Occluding  surface  defined 7 

Occlusion  line 189 

"        — relation  of  the  lower  and  upper  teeth 188 

"        — relative  mesio-distal  position  of  the  teeth 190 

Peridental  membrane 206 

Proximate  contact 195 

"        surfaces  defined .    5 

Pulp  chamber 152 

"        "        — abnormally  long  horns 185 

"         "        — conditions  which  cause  diminished  size 155 

"        "        — diminished  size  of,  in  the  adult 154 

"        "        — dissections  necessary  to  show 157 

"        "        — divisions 153 

"        "        — early  formative  stages 154 

"         "         — forms 153 

"         "        — in  single  rooted  teeth 156 

"        "        — lateral  openings 184 

"        "        of  the  upper  incisors 160 

"        "        "     "    lower        "        164 

"         "         "     "     upper  cuspids 163 

"        "         "     "    lower        "      165 

"         "         "     "    upper  first  bicuspid   167 

"        "     "         "      second  "         168 

"        "        "    "    lower  bicuspids 169 

"        "        "    "    upper  molars 172 

"        "         "     "    lower        "     180 

"        "        "    "    deciduous  teeth 186 

"        "        — secondary  formations 183 

"        "        — shortening  of  the  horns ,  - .  154 

"        "        — variations  in  the  form 183 

Eidges  defined 9 

"      — how  named , 9 

"      — marginal 9 

"      — transverse 9 

"      — triangular 9 

Eoots  of  the  teeth  defined 3 

Eoots  of  the  teeth — divisions 3 

Eoot  canal 153 

"        "     — distal,  of  the  lower  molars 182 

"        "    — distal,  of  the  upper  molars 176 

"        "     — lateral  openings 184 

"        "    — lingual,  of  the  upper  molars 174 


INDEX.  ix 

Root  canal — mesial,  of  the  upper  molars 175 

"        "    of  the  bicuspids,  lower 170 

"         "        ''            "          upper  first 167 

"        "        "            "              "      second 168 

"        "        "      cuspids,  lower 165 

"        "         "            "         upper 163 

"        "        "      incisors,  lower 164 

"        "        "             "       upper 161 

"        "         "      molars,  lower 181 

"        "         "            "      upper 173 

"        '     — size  of,  in  the  incisors 162 

"        "    — position  of,  in  the  upper  molars 173 

"         "    — upper  first  molar 173 

"        "    — upper  second  molar 177 

"        "    — upper  third  molar 178 

"         "    — variations  of  ihe,  in  the  upper  molars 177 

Short  cusped  teeth , 14 

Spaces,  inter-proximate 193 

"                "                 defined 13 

Sulcate  groove  defined 11 

Sulcus  defined 10 

Supplemental  grooves  defined 12 

Surfaces,  mesial  and  distal,  defined , 5 

"        occluding,  defined 7 

"        of  the  crown,  named 4 

"        proximate,  defined 5 

Tables  of  measurements  of  the  teeth 15 

Teeth — arrangement 187 

"    — number 2 

Thick-necked  teeth . .  14 

Tissues  of  the  teeth 2 

Tongue-tied 209 

Transverse  ridges  defined 9 

Triangular  ridges  defined 9 

Tubercle  defined 9 

Wrinkles  defined 12 


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Descriptive  anatomy  of  the  human  teeth. 


2002342324 


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